JAVA-12097: renamed algorithms-module to algorithms-modules

algorithms-modules/algorithms-miscellaneous-3/.gitignore

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+/target/
+.settings/
+.classpath
+.project

algorithms-modules/algorithms-miscellaneous-3/README.md

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+## Algorithms - Miscellaneous
+
+This module contains articles about algorithms. Some classes of algorithms, e.g., [sorting](/algorithms-sorting) and
+[genetic algorithms](/algorithms-genetic), have their own dedicated modules. 
+
+## Relevant Articles:
+
+- [Java Two Pointer Technique](https://www.baeldung.com/java-two-pointer-technique)
+- [Implementing Simple State Machines with Java Enums](https://www.baeldung.com/java-enum-simple-state-machine)
+- [Converting Between Roman and Arabic Numerals in Java](https://www.baeldung.com/java-convert-roman-arabic)
+- [Practical Java Examples of the Big O Notation](https://www.baeldung.com/java-algorithm-complexity)
+- [Checking If a List Is Sorted in Java](https://www.baeldung.com/java-check-if-list-sorted)
+- [Checking if a Java Graph has a Cycle](https://www.baeldung.com/java-graph-has-a-cycle)
+- [A Guide to the Folding Technique in Java](https://www.baeldung.com/folding-hashing-technique)
+- [Creating a Triangle with for Loops in Java](https://www.baeldung.com/java-print-triangle)
+- [The K-Means Clustering Algorithm in Java](https://www.baeldung.com/java-k-means-clustering-algorithm)
+- More articles: [[<-- prev]](/algorithms-miscellaneous-2) [[next -->]](/algorithms-miscellaneous-4)

algorithms-modules/algorithms-miscellaneous-3/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>algorithms-miscellaneous-3</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>algorithms-miscellaneous-3</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>algorithms-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>retrofit</artifactId>
+            <version>${retrofit.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.squareup.retrofit2</groupId>
+            <artifactId>converter-jackson</artifactId>
+            <version>${retrofit.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>pl.pragmatists</groupId>
+            <artifactId>JUnitParams</artifactId>
+            <version>${JUnitParams.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-bytecode</artifactId>
+            <version>${jmh-generator.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <retrofit.version>2.6.0</retrofit.version>
+        <JUnitParams.version>1.1.0</JUnitParams.version>
+    </properties>
+
+</project>

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/checksortedlist/Employee.java

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+package com.baeldung.algorithms.checksortedlist;
+
+public class Employee {
+
+    long id;
+
+    String name;
+
+    public Employee() {
+    }
+
+    public Employee(long id, String name) {
+        super();
+        this.id = id;
+        this.name = name;
+    }
+
+    public long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/checksortedlist/SortedListChecker.java

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+package com.baeldung.algorithms.checksortedlist;
+
+import static org.apache.commons.collections4.CollectionUtils.isEmpty;
+
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.List;
+
+import com.google.common.collect.Comparators;
+import com.google.common.collect.Ordering;;
+
+public class SortedListChecker {
+
+    private SortedListChecker() {
+        throw new AssertionError();
+    }
+
+    public static boolean checkIfSortedUsingIterativeApproach(List<String> listOfStrings) {
+        if (isEmpty(listOfStrings) || listOfStrings.size() == 1) {
+            return true;
+        }
+
+        Iterator<String> iter = listOfStrings.iterator();
+        String current, previous = iter.next();
+        while (iter.hasNext()) {
+            current = iter.next();
+            if (previous.compareTo(current) > 0) {
+                return false;
+            }
+            previous = current;
+        }
+        return true;
+    }
+
+    public static boolean checkIfSortedUsingIterativeApproach(List<Employee> employees, Comparator<Employee> employeeComparator) {
+        if (isEmpty(employees) || employees.size() == 1) {
+            return true;
+        }
+
+        Iterator<Employee> iter = employees.iterator();
+        Employee current, previous = iter.next();
+        while (iter.hasNext()) {
+            current = iter.next();
+            if (employeeComparator.compare(previous, current) > 0) {
+                return false;
+            }
+            previous = current;
+        }
+        return true;
+    }
+
+    public static boolean checkIfSortedUsingRecursion(List<String> listOfStrings) {
+        return isSortedRecursive(listOfStrings, listOfStrings.size());
+    }
+
+    public static boolean isSortedRecursive(List<String> listOfStrings, int index) {
+        if (index < 2) {
+            return true;
+        } else if (listOfStrings.get(index - 2)
+            .compareTo(listOfStrings.get(index - 1)) > 0) {
+            return false;
+        } else {
+            return isSortedRecursive(listOfStrings, index - 1);
+        }
+    }
+
+    public static boolean checkIfSortedUsingOrderingClass(List<String> listOfStrings) {
+        return Ordering.<String> natural()
+            .isOrdered(listOfStrings);
+    }
+
+    public static boolean checkIfSortedUsingOrderingClass(List<Employee> employees, Comparator<Employee> employeeComparator) {
+        return Ordering.from(employeeComparator)
+            .isOrdered(employees);
+    }
+
+    public static boolean checkIfSortedUsingOrderingClassHandlingNull(List<String> listOfStrings) {
+        return Ordering.<String> natural()
+            .nullsLast()
+            .isOrdered(listOfStrings);
+    }
+
+    public static boolean checkIfSortedUsingComparators(List<String> listOfStrings) {
+        return Comparators.isInOrder(listOfStrings, Comparator.<String> naturalOrder());
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/enumstatemachine/LeaveRequestState.java

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+package com.baeldung.algorithms.enumstatemachine;
+
+public enum LeaveRequestState {
+
+    Submitted {
+        @Override
+        public LeaveRequestState nextState() {
+            System.out.println("Starting the Leave Request and sending to Team Leader for approval.");
+            return Escalated;
+        }
+
+        @Override
+        public String responsiblePerson() {
+            return "Employee";
+        }
+    },
+    Escalated {
+        @Override
+        public LeaveRequestState nextState() {
+            System.out.println("Reviewing the Leave Request and escalating to Department Manager.");
+            return Approved;
+        }
+
+        @Override
+        public String responsiblePerson() {
+            return "Team Leader";
+        }
+    },
+    Approved {
+        @Override
+        public LeaveRequestState nextState() {
+            System.out.println("Approving the Leave Request.");
+            return this;
+        }
+
+        @Override
+        public String responsiblePerson() {
+            return "Department Manager";
+        }
+    };
+
+    public abstract String responsiblePerson();
+
+    public abstract LeaveRequestState nextState();
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/graphcycledetection/domain/Graph.java

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+package com.baeldung.algorithms.graphcycledetection.domain;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Graph {
+
+    private List<Vertex> vertices;
+
+    public Graph() {
+        this.vertices = new ArrayList<>();
+    }
+
+    public Graph(List<Vertex> vertices) {
+        this.vertices = vertices;
+    }
+
+    public void addVertex(Vertex vertex) {
+        this.vertices.add(vertex);
+    }
+
+    public void addEdge(Vertex from, Vertex to) {
+        from.addNeighbour(to);
+    }
+
+    public boolean hasCycle() {
+        for (Vertex vertex : vertices) {
+            if (!vertex.isVisited() && hasCycle(vertex)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public boolean hasCycle(Vertex sourceVertex) {
+        sourceVertex.setBeingVisited(true);
+
+        for (Vertex neighbour : sourceVertex.getAdjacencyList()) {
+            if (neighbour.isBeingVisited()) {
+                // backward edge exists
+                return true;
+            } else if (!neighbour.isVisited() && hasCycle(neighbour)) {
+                return true;
+            }
+        }
+
+        sourceVertex.setBeingVisited(false);
+        sourceVertex.setVisited(true);
+        return false;
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/graphcycledetection/domain/Vertex.java

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+package com.baeldung.algorithms.graphcycledetection.domain;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Vertex {
+
+    private String label;
+
+    private boolean visited;
+
+    private boolean beingVisited;
+
+    private List<Vertex> adjacencyList;
+
+    public Vertex(String label) {
+        this.label = label;
+        this.adjacencyList = new ArrayList<>();
+    }
+
+    public String getLabel() {
+        return label;
+    }
+
+    public void setLabel(String label) {
+        this.label = label;
+    }
+
+    public boolean isVisited() {
+        return visited;
+    }
+
+    public void setVisited(boolean visited) {
+        this.visited = visited;
+    }
+
+    public boolean isBeingVisited() {
+        return beingVisited;
+    }
+
+    public void setBeingVisited(boolean beingVisited) {
+        this.beingVisited = beingVisited;
+    }
+
+    public List<Vertex> getAdjacencyList() {
+        return adjacencyList;
+    }
+
+    public void setAdjacencyList(List<Vertex> adjacencyList) {
+        this.adjacencyList = adjacencyList;
+    }
+
+    public void addNeighbour(Vertex adjacent) {
+        this.adjacencyList.add(adjacent);
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Centroid.java

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+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Encapsulates all coordinates for a particular cluster centroid.
+ */
+public class Centroid {
+
+    /**
+     * The centroid coordinates.
+     */
+    private final Map<String, Double> coordinates;
+
+    public Centroid(Map<String, Double> coordinates) {
+        this.coordinates = coordinates;
+    }
+
+    public Map<String, Double> getCoordinates() {
+        return coordinates;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Centroid centroid = (Centroid) o;
+        return Objects.equals(getCoordinates(), centroid.getCoordinates());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getCoordinates());
+    }
+
+    @Override
+    public String toString() {
+        return "Centroid " + coordinates;
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Distance.java

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+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+
+/**
+ * Defines a contract to calculate distance between two feature vectors. The less the
+ * calculated distance, the more two items are similar to each other.
+ */
+public interface Distance {
+
+    /**
+     * Calculates the distance between two feature vectors.
+     *
+     * @param f1 The first set of features.
+     * @param f2 The second set of features.
+     * @return Calculated distance.
+     * @throws IllegalArgumentException If the given feature vectors are invalid.
+     */
+    double calculate(Map<String, Double> f1, Map<String, Double> f2);
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Errors.java

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+package com.baeldung.algorithms.kmeans;
+
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Encapsulates methods to calculates errors between centroid and the cluster members.
+ */
+public class Errors {
+
+    public static double sse(Map<Centroid, List<Record>> clustered, Distance distance) {
+        double sum = 0;
+        for (Map.Entry<Centroid, List<Record>> entry : clustered.entrySet()) {
+            Centroid centroid = entry.getKey();
+            for (Record record : entry.getValue()) {
+                double d = distance.calculate(centroid.getCoordinates(), record.getFeatures());
+                sum += Math.pow(d, 2);
+            }
+        }
+
+        return sum;
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/EuclideanDistance.java

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+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+
+/**
+ * Calculates the distance between two items using the Euclidean formula.
+ */
+public class EuclideanDistance implements Distance {
+
+    @Override
+    public double calculate(Map<String, Double> f1, Map<String, Double> f2) {
+        if (f1 == null || f2 == null) {
+            throw new IllegalArgumentException("Feature vectors can't be null");
+        }
+
+        double sum = 0;
+        for (String key : f1.keySet()) {
+            Double v1 = f1.get(key);
+            Double v2 = f2.get(key);
+
+            if (v1 != null && v2 != null) sum += Math.pow(v1 - v2, 2);
+        }
+
+        return Math.sqrt(sum);
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/KMeans.java

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+package com.baeldung.algorithms.kmeans;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.Set;
+
+import static java.util.stream.Collectors.toList;
+import static java.util.stream.Collectors.toSet;
+
+/**
+ * Encapsulates an implementation of KMeans clustering algorithm.
+ *
+ * @author Ali Dehghani
+ */
+public class KMeans {
+
+    private KMeans() {
+        throw new IllegalAccessError("You shouldn't call this constructor");
+    }
+
+    /**
+     * Will be used to generate random numbers.
+     */
+    private static final Random random = new Random();
+
+    /**
+     * Performs the K-Means clustering algorithm on the given dataset.
+     *
+     * @param records       The dataset.
+     * @param k             Number of Clusters.
+     * @param distance      To calculate the distance between two items.
+     * @param maxIterations Upper bound for the number of iterations.
+     * @return K clusters along with their features.
+     */
+    public static Map<Centroid, List<Record>> fit(List<Record> records, int k, Distance distance, int maxIterations) {
+        applyPreconditions(records, k, distance, maxIterations);
+
+        List<Centroid> centroids = randomCentroids(records, k);
+        Map<Centroid, List<Record>> clusters = new HashMap<>();
+        Map<Centroid, List<Record>> lastState = new HashMap<>();
+
+        // iterate for a pre-defined number of times
+        for (int i = 0; i < maxIterations; i++) {
+            boolean isLastIteration = i == maxIterations - 1;
+
+            // in each iteration we should find the nearest centroid for each record
+            for (Record record : records) {
+                Centroid centroid = nearestCentroid(record, centroids, distance);
+                assignToCluster(clusters, record, centroid);
+            }
+
+            // if the assignment does not change, then the algorithm terminates
+            boolean shouldTerminate = isLastIteration || clusters.equals(lastState);
+            lastState = clusters;
+            if (shouldTerminate) {
+                break;
+            }
+
+            // at the end of each iteration we should relocate the centroids
+            centroids = relocateCentroids(clusters);
+            clusters = new HashMap<>();
+        }
+
+        return lastState;
+    }
+
+    /**
+     * Move all cluster centroids to the average of all assigned features.
+     *
+     * @param clusters The current cluster configuration.
+     * @return Collection of new and relocated centroids.
+     */
+    private static List<Centroid> relocateCentroids(Map<Centroid, List<Record>> clusters) {
+        return clusters
+          .entrySet()
+          .stream()
+          .map(e -> average(e.getKey(), e.getValue()))
+          .collect(toList());
+    }
+
+    /**
+     * Moves the given centroid to the average position of all assigned features. If
+     * the centroid has no feature in its cluster, then there would be no need for a
+     * relocation. Otherwise, for each entry we calculate the average of all records
+     * first by summing all the entries and then dividing the final summation value by
+     * the number of records.
+     *
+     * @param centroid The centroid to move.
+     * @param records  The assigned features.
+     * @return The moved centroid.
+     */
+    private static Centroid average(Centroid centroid, List<Record> records) {
+        // if this cluster is empty, then we shouldn't move the centroid
+        if (records == null || records.isEmpty()) {
+            return centroid;
+        }
+
+        // Since some records don't have all possible attributes, we initialize
+        // average coordinates equal to current centroid coordinates
+        Map<String, Double> average = centroid.getCoordinates();
+
+        // The average function works correctly if we clear all coordinates corresponding
+        // to present record attributes
+        records
+          .stream()
+          .flatMap(e -> e
+            .getFeatures()
+            .keySet()
+            .stream())
+          .forEach(k -> average.put(k, 0.0));
+
+        for (Record record : records) {
+            record
+              .getFeatures()
+              .forEach((k, v) -> average.compute(k, (k1, currentValue) -> v + currentValue));
+        }
+
+        average.forEach((k, v) -> average.put(k, v / records.size()));
+
+        return new Centroid(average);
+    }
+
+    /**
+     * Assigns a feature vector to the given centroid. If this is the first assignment for this centroid,
+     * first we should create the list.
+     *
+     * @param clusters The current cluster configuration.
+     * @param record   The feature vector.
+     * @param centroid The centroid.
+     */
+    private static void assignToCluster(Map<Centroid, List<Record>> clusters, Record record, Centroid centroid) {
+        clusters.compute(centroid, (key, list) -> {
+            if (list == null) {
+                list = new ArrayList<>();
+            }
+
+            list.add(record);
+            return list;
+        });
+    }
+
+    /**
+     * With the help of the given distance calculator, iterates through centroids and finds the
+     * nearest one to the given record.
+     *
+     * @param record    The feature vector to find a centroid for.
+     * @param centroids Collection of all centroids.
+     * @param distance  To calculate the distance between two items.
+     * @return The nearest centroid to the given feature vector.
+     */
+    private static Centroid nearestCentroid(Record record, List<Centroid> centroids, Distance distance) {
+        double minimumDistance = Double.MAX_VALUE;
+        Centroid nearest = null;
+
+        for (Centroid centroid : centroids) {
+            double currentDistance = distance.calculate(record.getFeatures(), centroid.getCoordinates());
+
+            if (currentDistance < minimumDistance) {
+                minimumDistance = currentDistance;
+                nearest = centroid;
+            }
+        }
+
+        return nearest;
+    }
+
+    /**
+     * Generates k random centroids. Before kicking-off the centroid generation process,
+     * first we calculate the possible value range for each attribute. Then when
+     * we're going to generate the centroids, we generate random coordinates in
+     * the [min, max] range for each attribute.
+     *
+     * @param records The dataset which helps to calculate the [min, max] range for
+     *                each attribute.
+     * @param k       Number of clusters.
+     * @return Collections of randomly generated centroids.
+     */
+    private static List<Centroid> randomCentroids(List<Record> records, int k) {
+        List<Centroid> centroids = new ArrayList<>();
+        Map<String, Double> maxs = new HashMap<>();
+        Map<String, Double> mins = new HashMap<>();
+
+        for (Record record : records) {
+            record
+              .getFeatures()
+              .forEach((key, value) -> {
+                  // compares the value with the current max and choose the bigger value between them
+                  maxs.compute(key, (k1, max) -> max == null || value > max ? value : max);
+
+                  // compare the value with the current min and choose the smaller value between them
+                  mins.compute(key, (k1, min) -> min == null || value < min ? value : min);
+              });
+        }
+
+        Set<String> attributes = records
+          .stream()
+          .flatMap(e -> e
+            .getFeatures()
+            .keySet()
+            .stream())
+          .collect(toSet());
+        for (int i = 0; i < k; i++) {
+            Map<String, Double> coordinates = new HashMap<>();
+            for (String attribute : attributes) {
+                double max = maxs.get(attribute);
+                double min = mins.get(attribute);
+                coordinates.put(attribute, random.nextDouble() * (max - min) + min);
+            }
+
+            centroids.add(new Centroid(coordinates));
+        }
+
+        return centroids;
+    }
+
+    private static void applyPreconditions(List<Record> records, int k, Distance distance, int maxIterations) {
+        if (records == null || records.isEmpty()) {
+            throw new IllegalArgumentException("The dataset can't be empty");
+        }
+
+        if (k <= 1) {
+            throw new IllegalArgumentException("It doesn't make sense to have less than or equal to 1 cluster");
+        }
+
+        if (distance == null) {
+            throw new IllegalArgumentException("The distance calculator is required");
+        }
+
+        if (maxIterations <= 0) {
+            throw new IllegalArgumentException("Max iterations should be a positive number");
+        }
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/LastFm.java

@@ -0,0 +1,144 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import okhttp3.OkHttpClient;
+import retrofit2.Retrofit;
+import retrofit2.converter.jackson.JacksonConverterFactory;
+
+import static java.util.stream.Collectors.toSet;
+
+public class LastFm {
+
+    private static OkHttpClient okHttp = new OkHttpClient.Builder()
+      .addInterceptor(new LastFmService.Authenticator("put your API key here"))
+      .build();
+
+    private static Retrofit retrofit = new Retrofit.Builder()
+      .client(okHttp)
+      .addConverterFactory(JacksonConverterFactory.create())
+      .baseUrl("http://ws.audioscrobbler.com/")
+      .build();
+
+    private static LastFmService lastFm = retrofit.create(LastFmService.class);
+
+    private static ObjectMapper mapper = new ObjectMapper();
+
+    public static void main(String[] args) throws IOException {
+        List<String> artists = getTop100Artists();
+        Set<String> tags = getTop100Tags();
+        List<Record> records = datasetWithTaggedArtists(artists, tags);
+
+        Map<Centroid, List<Record>> clusters = KMeans.fit(records, 7, new EuclideanDistance(), 1000);
+        // Print the cluster configuration
+        clusters.forEach((key, value) -> {
+            System.out.println("------------------------------ CLUSTER -----------------------------------");
+
+            System.out.println(sortedCentroid(key));
+            String members = String.join(", ", value
+              .stream()
+              .map(Record::getDescription)
+              .collect(toSet()));
+            System.out.print(members);
+
+            System.out.println();
+            System.out.println();
+        });
+
+        Map<String, Object> json = convertToD3CompatibleMap(clusters);
+        System.out.println(mapper.writeValueAsString(json));
+    }
+
+    private static Map<String, Object> convertToD3CompatibleMap(Map<Centroid, List<Record>> clusters) {
+        Map<String, Object> json = new HashMap<>();
+        json.put("name", "Musicians");
+        List<Map<String, Object>> children = new ArrayList<>();
+        clusters.forEach((key, value) -> {
+            Map<String, Object> child = new HashMap<>();
+            child.put("name", dominantGenre(sortedCentroid(key)));
+            List<Map<String, String>> nested = new ArrayList<>();
+            for (Record record : value) {
+                nested.add(Collections.singletonMap("name", record.getDescription()));
+            }
+            child.put("children", nested);
+
+            children.add(child);
+        });
+        json.put("children", children);
+        return json;
+    }
+
+    private static String dominantGenre(Centroid centroid) {
+        return centroid
+          .getCoordinates()
+          .keySet()
+          .stream()
+          .limit(2)
+          .collect(Collectors.joining(", "));
+    }
+
+    private static Centroid sortedCentroid(Centroid key) {
+        List<Map.Entry<String, Double>> entries = new ArrayList<>(key
+          .getCoordinates()
+          .entrySet());
+        entries.sort((e1, e2) -> e2
+          .getValue()
+          .compareTo(e1.getValue()));
+
+        Map<String, Double> sorted = new LinkedHashMap<>();
+        for (Map.Entry<String, Double> entry : entries) {
+            sorted.put(entry.getKey(), entry.getValue());
+        }
+
+        return new Centroid(sorted);
+    }
+
+    private static List<Record> datasetWithTaggedArtists(List<String> artists, Set<String> topTags) throws IOException {
+        List<Record> records = new ArrayList<>();
+        for (String artist : artists) {
+            Map<String, Double> tags = lastFm
+              .topTagsFor(artist)
+              .execute()
+              .body()
+              .all();
+
+            // Only keep popular tags.
+            tags
+              .entrySet()
+              .removeIf(e -> !topTags.contains(e.getKey()));
+
+            records.add(new Record(artist, tags));
+        }
+        return records;
+    }
+
+    private static Set<String> getTop100Tags() throws IOException {
+        return lastFm
+          .topTags()
+          .execute()
+          .body()
+          .all();
+    }
+
+    private static List<String> getTop100Artists() throws IOException {
+        List<String> artists = new ArrayList<>();
+        for (int i = 1; i <= 2; i++) {
+            artists.addAll(lastFm
+              .topArtists(i)
+              .execute()
+              .body()
+              .all());
+        }
+
+        return artists;
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/LastFmService.java

@@ -0,0 +1,118 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import okhttp3.HttpUrl;
+import okhttp3.Interceptor;
+import okhttp3.Request;
+import okhttp3.Response;
+import retrofit2.Call;
+import retrofit2.http.GET;
+import retrofit2.http.Query;
+
+import static com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.ANY;
+import static java.util.stream.Collectors.toList;
+
+public interface LastFmService {
+
+    @GET("/2.0/?method=chart.gettopartists&format=json&limit=50")
+    Call<Artists> topArtists(@Query("page") int page);
+
+    @GET("/2.0/?method=artist.gettoptags&format=json&limit=20&autocorrect=1")
+    Call<Tags> topTagsFor(@Query("artist") String artist);
+
+    @GET("/2.0/?method=chart.gettoptags&format=json&limit=100")
+    Call<TopTags> topTags();
+
+    /**
+     * HTTP interceptor to intercept all HTTP requests and add the API key to them.
+     */
+    class Authenticator implements Interceptor {
+
+        private final String apiKey;
+
+        Authenticator(String apiKey) {
+            this.apiKey = apiKey;
+        }
+
+        @Override
+        public Response intercept(Chain chain) throws IOException {
+            HttpUrl url = chain
+              .request()
+              .url()
+              .newBuilder()
+              .addQueryParameter("api_key", apiKey)
+              .build();
+            Request request = chain
+              .request()
+              .newBuilder()
+              .url(url)
+              .build();
+
+            return chain.proceed(request);
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class TopTags {
+
+        private Map<String, Object> tags;
+
+        @SuppressWarnings("unchecked")
+        public Set<String> all() {
+            List<Map<String, Object>> topTags = (List<Map<String, Object>>) tags.get("tag");
+            return topTags
+              .stream()
+              .map(e -> ((String) e.get("name")))
+              .collect(Collectors.toSet());
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class Tags {
+
+        @JsonProperty("toptags") private Map<String, Object> topTags;
+
+        @SuppressWarnings("unchecked")
+        public Map<String, Double> all() {
+            try {
+                Map<String, Double> all = new HashMap<>();
+                List<Map<String, Object>> tags = (List<Map<String, Object>>) topTags.get("tag");
+                for (Map<String, Object> tag : tags) {
+                    all.put(((String) tag.get("name")), ((Integer) tag.get("count")).doubleValue());
+                }
+
+                return all;
+            } catch (Exception e) {
+                return Collections.emptyMap();
+            }
+        }
+    }
+
+    @JsonAutoDetect(fieldVisibility = ANY)
+    class Artists {
+
+        private Map<String, Object> artists;
+
+        @SuppressWarnings("unchecked")
+        public List<String> all() {
+            try {
+                List<Map<String, Object>> artists = (List<Map<String, Object>>) this.artists.get("artist");
+                return artists
+                  .stream()
+                  .map(e -> ((String) e.get("name")))
+                  .collect(toList());
+            } catch (Exception e) {
+                return Collections.emptyList();
+            }
+        }
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/kmeans/Record.java

@@ -0,0 +1,65 @@
+package com.baeldung.algorithms.kmeans;
+
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Encapsulates all feature values for a few attributes. Optionally each record
+ * can be described with the {@link #description} field.
+ */
+public class Record {
+
+    /**
+     * The record description. For example, this can be the artist name for the famous musician
+     * example.
+     */
+    private final String description;
+
+    /**
+     * Encapsulates all attributes and their corresponding values, i.e. features.
+     */
+    private final Map<String, Double> features;
+
+    public Record(String description, Map<String, Double> features) {
+        this.description = description;
+        this.features = features;
+    }
+
+    public Record(Map<String, Double> features) {
+        this("", features);
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public Map<String, Double> getFeatures() {
+        return features;
+    }
+
+    @Override
+    public String toString() {
+        String prefix = description == null || description
+          .trim()
+          .isEmpty() ? "Record" : description;
+
+        return prefix + ": " + features;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        Record record = (Record) o;
+        return Objects.equals(getDescription(), record.getDescription()) && Objects.equals(getFeatures(), record.getFeatures());
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(getDescription(), getFeatures());
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/printtriangles/PrintTriangleExamples.java

@@ -0,0 +1,61 @@
+package com.baeldung.algorithms.printtriangles;
+
+import org.apache.commons.lang3.StringUtils;
+
+public class PrintTriangleExamples {
+
+    public static String printARightTriangle(int N) {
+        StringBuilder result = new StringBuilder();
+        for (int r = 1; r <= N; r++) {
+            for (int j = 1; j <= r; j++) {
+                result.append("*");
+            }
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static String printAnIsoscelesTriangle(int N) {
+        StringBuilder result = new StringBuilder();
+        for (int r = 1; r <= N; r++) {
+            for (int sp = 1; sp <= N - r; sp++) {
+                result.append(" ");
+            }
+            for (int c = 1; c <= (r * 2) - 1; c++) {
+                result.append("*");
+            }
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static String printAnIsoscelesTriangleUsingStringUtils(int N) {
+        StringBuilder result = new StringBuilder();
+
+        for (int r = 1; r <= N; r++) {
+            result.append(StringUtils.repeat(' ', N - r));
+            result.append(StringUtils.repeat('*', 2 * r - 1));
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static String printAnIsoscelesTriangleUsingSubstring(int N) {
+        StringBuilder result = new StringBuilder();
+        String helperString = StringUtils.repeat(' ', N - 1) + StringUtils.repeat('*', N * 2 - 1);
+
+        for (int r = 0; r < N; r++) {
+            result.append(helperString.substring(r, N + 2 * r));
+            result.append(System.lineSeparator());
+        }
+        return result.toString();
+    }
+
+    public static void main(String[] args) {
+        System.out.println(printARightTriangle(5));
+        System.out.println(printAnIsoscelesTriangle(5));
+        System.out.println(printAnIsoscelesTriangleUsingStringUtils(5));
+        System.out.println(printAnIsoscelesTriangleUsingSubstring(5));
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/romannumerals/RomanArabicConverter.java

@@ -0,0 +1,52 @@
+package com.baeldung.algorithms.romannumerals;
+
+import java.util.List;
+
+class RomanArabicConverter {
+
+    public static int romanToArabic(String input) {
+        String romanNumeral = input.toUpperCase();
+        int result = 0;
+        
+        List<RomanNumeral> romanNumerals = RomanNumeral.getReverseSortedValues();
+
+        int i = 0;
+
+        while ((romanNumeral.length() > 0) && (i < romanNumerals.size())) {
+            RomanNumeral symbol = romanNumerals.get(i);
+            if (romanNumeral.startsWith(symbol.name())) {
+                result += symbol.getValue();
+                romanNumeral = romanNumeral.substring(symbol.name().length());
+            } else {
+                i++;
+            }
+        }
+        if (romanNumeral.length() > 0) {
+            throw new IllegalArgumentException(input + " cannot be converted to a Roman Numeral");
+        }
+
+        return result;
+    }
+
+    public static String arabicToRoman(int number) {
+        if ((number <= 0) || (number > 4000)) {
+            throw new IllegalArgumentException(number + " is not in range (0,4000]");
+        }
+
+        List<RomanNumeral> romanNumerals = RomanNumeral.getReverseSortedValues();
+
+        int i = 0;
+        StringBuilder sb = new StringBuilder();
+
+        while (number > 0 && i < romanNumerals.size()) {
+            RomanNumeral currentSymbol = romanNumerals.get(i);
+            if (currentSymbol.getValue() <= number) {
+                sb.append(currentSymbol.name());
+                number -= currentSymbol.getValue();
+            } else {
+                i++;
+            }
+        }
+        return sb.toString();
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/romannumerals/RomanNumeral.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.romannumerals;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+enum RomanNumeral {
+    I(1), IV(4), V(5), IX(9), X(10), XL(40), L(50), XC(90), C(100), CD(400), D(500), CM(900), M(1000);
+
+    private int value;
+
+    RomanNumeral(int value) {
+        this.value = value;
+    }
+
+    public int getValue() {
+        return value;
+    }
+    
+    public static List<RomanNumeral> getReverseSortedValues() {
+        return Arrays.stream(values())
+          .sorted(Comparator.comparing((RomanNumeral e) -> e.value).reversed())
+          .collect(Collectors.toList());
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddle.java

@@ -0,0 +1,16 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class LinkedListFindMiddle {
+
+    public <T> T findMiddle(MyNode<T> head) {
+        MyNode<T> slowPointer = head;
+        MyNode<T> fastPointer = head;
+
+        while (fastPointer.next != null && fastPointer.next.next != null) {
+            fastPointer = fastPointer.next.next;
+            slowPointer = slowPointer.next;
+        }
+        return slowPointer.data;
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/twopointertechnique/MyNode.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class MyNode<E> {
+    MyNode<E> next;
+    E data;
+
+    public MyNode(E value) {
+        data = value;
+        next = null;
+    }
+
+    public MyNode(E value, MyNode<E> n) {
+        data = value;
+        next = n;
+    }
+
+    public void setNext(MyNode<E> n) {
+        next = n;
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/twopointertechnique/RotateArray.java

@@ -0,0 +1,22 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class RotateArray {
+
+    public void rotate(int[] input, int step) {
+        step %= input.length;
+        reverse(input, 0, input.length - 1);
+        reverse(input, 0, step - 1);
+        reverse(input, step, input.length - 1);
+    }
+
+    private void reverse(int[] input, int start, int end) {
+        while (start < end) {
+            int temp = input[start];
+            input[start] = input[end];
+            input[end] = temp;
+            start++;
+            end--;
+        }
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/twopointertechnique/TwoSum.java

@@ -0,0 +1,38 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+public class TwoSum {
+
+    public boolean twoSum(int[] input, int targetValue) {
+
+        int pointerOne = 0;
+        int pointerTwo = input.length - 1;
+
+        while (pointerOne < pointerTwo) {
+            int sum = input[pointerOne] + input[pointerTwo];
+
+            if (sum == targetValue) {
+                return true;
+            } else if (sum < targetValue) {
+                pointerOne++;
+            } else {
+                pointerTwo--;
+            }
+        }
+
+        return false;
+    }
+
+    public boolean twoSumSlow(int[] input, int targetValue) {
+
+        for (int i = 0; i < input.length; i++) {
+            for (int j = 1; j < input.length; j++) {
+                if (input[i] + input[j] == targetValue) {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/folding/FoldingHash.java

@@ -0,0 +1,78 @@
+package com.baeldung.folding;
+
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+/**
+ * Calculate a hash value for the strings using the folding technique.
+ * 
+ * The implementation serves only to the illustration purposes and is far
+ * from being the most efficient. 
+ * 
+ * @author A.Shcherbakov
+ *
+ */
+public class FoldingHash {
+
+    /**
+     * Calculate the hash value of a given string.
+     * 
+     * @param str Assume it is not null
+     * @param groupSize the group size in the folding technique
+     * @param maxValue defines a max value that the hash may acquire (exclusive)     
+     * @return integer value from 0 (inclusive) to maxValue (exclusive)
+     */
+    public int hash(String str, int groupSize, int maxValue) {
+        final int[] codes = this.toAsciiCodes(str);
+        return IntStream.range(0, str.length())
+            .filter(i -> i % groupSize == 0)
+            .mapToObj(i -> extract(codes, i, groupSize))
+            .map(block -> concatenate(block))
+            .reduce(0, (a, b) -> (a + b) % maxValue);
+    }
+
+    /**
+     * Returns a new array of given length whose elements are take from 
+     * the original one starting from the offset.
+     *  
+     * If the original array has not enough elements, the returning array will contain 
+     * element from the offset till the end of the original array.
+     *  
+     * @param numbers original array. Assume it is not null.
+     * @param offset index of the element to start from. Assume it is less than the size of the array 
+     * @param length max size of the resulting array
+     * @return
+     */
+    public int[] extract(int[] numbers, int offset, int length) {
+        final int defect = numbers.length - (offset + length);
+        final int s = defect < 0 ? length + defect : length;
+        int[] result = new int[s];
+        for (int index = 0; index < s; index++) {
+            result[index] = numbers[index + offset];
+        }
+        return result;
+    }
+
+    /**
+     * Concatenate the numbers into a single number as if they were strings.
+     * Assume that the procedure does not suffer from the overflow.
+     * @param numbers integers to concatenate
+     * @return
+     */
+    public int concatenate(int[] numbers) {
+        final String merged = IntStream.of(numbers)
+            .mapToObj(number -> "" + number)
+            .collect(Collectors.joining());
+        return Integer.parseInt(merged, 10);
+    }
+
+    /**
+     * Convert the string into its characters' ASCII codes.
+     * @param str input string
+     * @return
+     */
+    private int[] toAsciiCodes(String str) {
+        return str.chars()
+            .toArray();
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/java/com/baeldung/folding/Main.java

@@ -0,0 +1,17 @@
+package com.baeldung.folding;
+
+/**
+ * Code snippet for article "A Guide to the Folding Technique".
+ *  
+ * @author A.Shcherbakov
+ *
+ */
+public class Main {
+
+    public static void main(String... arg) {
+        FoldingHash hasher = new FoldingHash();
+        final String str = "Java language";
+        System.out.println(hasher.hash(str, 2, 100_000));
+        System.out.println(hasher.hash(str, 3, 1_000));
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/resources/kmeans/lastfm.json

@@ -0,0 +1,490 @@
+{
+  "children": [
+    {
+      "children": [
+        {
+          "name": "Radiohead"
+        },
+        {
+          "name": "Red Hot Chili Peppers"
+        },
+        {
+          "name": "Coldplay"
+        },
+        {
+          "name": "Nirvana"
+        },
+        {
+          "name": "Panic! at the Disco"
+        },
+        {
+          "name": "The Cure"
+        },
+        {
+          "name": "Linkin Park"
+        },
+        {
+          "name": "Radiohead"
+        },
+        {
+          "name": "Red Hot Chili Peppers"
+        },
+        {
+          "name": "Coldplay"
+        },
+        {
+          "name": "Nirvana"
+        },
+        {
+          "name": "Panic! at the Disco"
+        },
+        {
+          "name": "The Cure"
+        },
+        {
+          "name": "Linkin Park"
+        },
+        {
+          "name": "Muse"
+        },
+        {
+          "name": "Maroon 5"
+        },
+        {
+          "name": "Foo Fighters"
+        },
+        {
+          "name": "Paramore"
+        },
+        {
+          "name": "Oasis"
+        },
+        {
+          "name": "Fall Out Boy"
+        },
+        {
+          "name": "OneRepublic"
+        },
+        {
+          "name": "Weezer"
+        },
+        {
+          "name": "System of a Down"
+        },
+        {
+          "name": "The White Stripes"
+        }
+      ],
+      "name": "rock, alternative"
+    },
+    {
+      "children": [
+        {
+          "name": "Lil Nas X"
+        },
+        {
+          "name": "Post Malone"
+        },
+        {
+          "name": "Drake"
+        },
+        {
+          "name": "Kanye West"
+        },
+        {
+          "name": "Kendrick Lamar"
+        },
+        {
+          "name": "Tyler, the Creator"
+        },
+        {
+          "name": "Eminem"
+        },
+        {
+          "name": "Childish Gambino"
+        },
+        {
+          "name": "Frank Ocean"
+        },
+        {
+          "name": "Lil Nas X"
+        },
+        {
+          "name": "Post Malone"
+        },
+        {
+          "name": "Drake"
+        },
+        {
+          "name": "Kanye West"
+        },
+        {
+          "name": "Kendrick Lamar"
+        },
+        {
+          "name": "Tyler, the Creator"
+        },
+        {
+          "name": "Eminem"
+        },
+        {
+          "name": "Childish Gambino"
+        },
+        {
+          "name": "Frank Ocean"
+        },
+        {
+          "name": "Lizzo"
+        },
+        {
+          "name": "Travi$ Scott"
+        },
+        {
+          "name": "A$AP Rocky"
+        },
+        {
+          "name": "Nicki Minaj"
+        },
+        {
+          "name": "xxxtentacion"
+        }
+      ],
+      "name": "Hip-Hop, rap"
+    },
+    {
+      "children": [
+        {
+          "name": "Arctic Monkeys"
+        },
+        {
+          "name": "Imagine Dragons"
+        },
+        {
+          "name": "The Killers"
+        },
+        {
+          "name": "Gorillaz"
+        },
+        {
+          "name": "The Black Keys"
+        },
+        {
+          "name": "Arctic Monkeys"
+        },
+        {
+          "name": "Imagine Dragons"
+        },
+        {
+          "name": "The Killers"
+        },
+        {
+          "name": "Gorillaz"
+        },
+        {
+          "name": "The Black Keys"
+        },
+        {
+          "name": "Twenty One Pilots"
+        },
+        {
+          "name": "Ellie Goulding"
+        },
+        {
+          "name": "Florence + the Machine"
+        },
+        {
+          "name": "Vampire Weekend"
+        },
+        {
+          "name": "The Smiths"
+        },
+        {
+          "name": "The Strokes"
+        },
+        {
+          "name": "MGMT"
+        },
+        {
+          "name": "Foster the People"
+        },
+        {
+          "name": "Two Door Cinema Club"
+        },
+        {
+          "name": "Cage the Elephant"
+        },
+        {
+          "name": "Arcade Fire"
+        },
+        {
+          "name": "The 1975"
+        }
+      ],
+      "name": "indie, alternative"
+    },
+    {
+      "children": [
+        {
+          "name": "Ed Sheeran"
+        },
+        {
+          "name": "Tame Impala"
+        },
+        {
+          "name": "Ed Sheeran"
+        },
+        {
+          "name": "Tame Impala"
+        },
+        {
+          "name": "Green Day"
+        },
+        {
+          "name": "Metallica"
+        },
+        {
+          "name": "blink-182"
+        },
+        {
+          "name": "Bon Iver"
+        },
+        {
+          "name": "The Clash"
+        }
+      ],
+      "name": "rock, punk rock"
+    },
+    {
+      "children": [
+        {
+          "name": "Calvin Harris"
+        },
+        {
+          "name": "The Weeknd"
+        },
+        {
+          "name": "The Chainsmokers"
+        },
+        {
+          "name": "Daft Punk"
+        },
+        {
+          "name": "Marshmello"
+        },
+        {
+          "name": "David Guetta"
+        },
+        {
+          "name": "Calvin Harris"
+        },
+        {
+          "name": "The Weeknd"
+        },
+        {
+          "name": "The Chainsmokers"
+        },
+        {
+          "name": "Daft Punk"
+        },
+        {
+          "name": "Marshmello"
+        },
+        {
+          "name": "David Guetta"
+        },
+        {
+          "name": "Avicii"
+        },
+        {
+          "name": "Kygo"
+        },
+        {
+          "name": "Martin Garrix"
+        },
+        {
+          "name": "Major Lazer"
+        },
+        {
+          "name": "Depeche Mode"
+        }
+      ],
+      "name": "electronic, dance"
+    },
+    {
+      "children": [
+        {
+          "name": "Queen"
+        },
+        {
+          "name": "The Beatles"
+        },
+        {
+          "name": "David Bowie"
+        },
+        {
+          "name": "Fleetwood Mac"
+        },
+        {
+          "name": "Pink Floyd"
+        },
+        {
+          "name": "The Rolling Stones"
+        },
+        {
+          "name": "Led Zeppelin"
+        },
+        {
+          "name": "Queen"
+        },
+        {
+          "name": "The Beatles"
+        },
+        {
+          "name": "David Bowie"
+        },
+        {
+          "name": "Fleetwood Mac"
+        },
+        {
+          "name": "Pink Floyd"
+        },
+        {
+          "name": "The Rolling Stones"
+        },
+        {
+          "name": "Led Zeppelin"
+        },
+        {
+          "name": "Elton John"
+        }
+      ],
+      "name": "classic rock, rock"
+    },
+    {
+      "children": [
+        {
+          "name": "Billie Eilish"
+        },
+        {
+          "name": "Ariana Grande"
+        },
+        {
+          "name": "Taylor Swift"
+        },
+        {
+          "name": "Beyoncé"
+        },
+        {
+          "name": "Shawn Mendes"
+        },
+        {
+          "name": "Rihanna"
+        },
+        {
+          "name": "Lana Del Rey"
+        },
+        {
+          "name": "Katy Perry"
+        },
+        {
+          "name": "Lady Gaga"
+        },
+        {
+          "name": "Miley Cyrus"
+        },
+        {
+          "name": "Mark Ronson"
+        },
+        {
+          "name": "Madonna"
+        },
+        {
+          "name": "Lorde"
+        },
+        {
+          "name": "Khalid"
+        },
+        {
+          "name": "Billie Eilish"
+        },
+        {
+          "name": "Ariana Grande"
+        },
+        {
+          "name": "Taylor Swift"
+        },
+        {
+          "name": "Beyoncé"
+        },
+        {
+          "name": "Shawn Mendes"
+        },
+        {
+          "name": "Rihanna"
+        },
+        {
+          "name": "Lana Del Rey"
+        },
+        {
+          "name": "Katy Perry"
+        },
+        {
+          "name": "Lady Gaga"
+        },
+        {
+          "name": "Miley Cyrus"
+        },
+        {
+          "name": "Mark Ronson"
+        },
+        {
+          "name": "Madonna"
+        },
+        {
+          "name": "Lorde"
+        },
+        {
+          "name": "Khalid"
+        },
+        {
+          "name": "Sia"
+        },
+        {
+          "name": "Sam Smith"
+        },
+        {
+          "name": "Halsey"
+        },
+        {
+          "name": "Michael Jackson"
+        },
+        {
+          "name": "Charli XCX"
+        },
+        {
+          "name": "Britney Spears"
+        },
+        {
+          "name": "Dua Lipa"
+        },
+        {
+          "name": "Jonas Brothers"
+        },
+        {
+          "name": "Bruno Mars"
+        },
+        {
+          "name": "Carly Rae Jepsen"
+        },
+        {
+          "name": "P!nk"
+        },
+        {
+          "name": "Adele"
+        }
+      ],
+      "name": "pop, female vocalists"
+    }
+  ],
+  "name": "Musicians"
+}

algorithms-modules/algorithms-miscellaneous-3/src/main/resources/kmeans/radial.html

@@ -0,0 +1,68 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<style>
+    .node circle {
+        fill: #fff;
+        stroke: steelblue;
+        stroke-width: 1.5px;
+    }
+
+    .node {
+        font: 10px sans-serif;
+    }
+
+    .link {
+        fill: none;
+        stroke: #ccc;
+        stroke-width: 1.5px;
+    }
+</style>
+<body>
+<script src="http://d3js.org/d3.v3.min.js"></script>
+<script>
+    var diameter = 1100;
+    var tree = d3.layout.tree()
+        .size([360, diameter / 2 - 300])
+        .separation(function (a, b) {
+            return (a.parent == b.parent ? 1 : 2) / a.depth;
+        });
+    var diagonal = d3.svg.diagonal.radial()
+        .projection(function (d) {
+            return [d.y, d.x / 180 * Math.PI];
+        });
+    var svg = d3.select("body").append("svg")
+        .attr("width", diameter)
+        .attr("height", diameter - 150)
+        .append("g")
+        .attr("transform", "translate(" + diameter / 2 + "," + diameter / 2 + ")");
+    d3.json("lastfm.json", function (error, root) {
+        var nodes = tree.nodes(root),
+            links = tree.links(nodes);
+        var link = svg.selectAll(".link")
+            .data(links)
+            .enter().append("path")
+            .attr("class", "link")
+            .attr("d", diagonal);
+        var node = svg.selectAll(".node")
+            .data(nodes)
+            .enter().append("g")
+            .attr("class", "node")
+            .attr("transform", function (d) {
+                return "rotate(" + (d.x - 90) + ")translate(" + d.y + ")";
+            })
+        node.append("circle")
+            .attr("r", 4.5);
+        node.append("text")
+            .attr("dy", ".31em")
+            .attr("text-anchor", function (d) {
+                return d.x < 180 ? "start" : "end";
+            })
+            .attr("transform", function (d) {
+                return d.x < 180 ? "translate(8)" : "rotate(180)translate(-8)";
+            })
+            .text(function (d) {
+                return d.name;
+            });
+    });
+    d3.select(self.frameElement).style("height", diameter - 150 + "px");
+</script>

algorithms-modules/algorithms-miscellaneous-3/src/main/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/analysis/AnalysisRunnerLiveTest.java

@@ -0,0 +1,139 @@
+package com.baeldung.algorithms.analysis;
+
+import org.junit.Test;
+
+public class AnalysisRunnerLiveTest {
+
+    int n = 10;
+    int total = 0;
+
+    @Test
+    public void whenConstantComplexity_thenConstantRuntime() {
+
+        System.out.println("**** n = " + n + " ****");
+        System.out.println();
+
+        // Constant Time
+        System.out.println("**** Constant time ****");
+
+        System.out.println("Hey - your input is: " + n);
+        System.out.println("Running time not dependent on input size!");
+        System.out.println();
+    }
+
+    @Test
+    public void whenLogarithmicComplexity_thenLogarithmicRuntime() {
+        // Logarithmic Time
+        System.out.println("**** Logarithmic Time ****");
+        for (int i = 1; i < n; i = i * 2) {
+            // System.out.println("Hey - I'm busy looking at: " + i);
+            total++;
+        }
+        System.out.println("Total amount of times run: " + total);
+        System.out.println();
+    }
+
+    @Test
+    public void whenLinearComplexity_thenLinearRuntime() {
+        // Linear Time
+        System.out.println("**** Linear Time ****");
+        for (int i = 0; i < n; i++) {
+            // System.out.println("Hey - I'm busy looking at: " + i);
+            total++;
+        }
+        System.out.println("Total amount of times run: " + total);
+        System.out.println();
+
+    }
+
+    @Test
+    public void whenNLogNComplexity_thenNLogNRuntime() {
+        // N Log N Time
+        System.out.println("**** nlogn Time ****");
+        total = 0;
+        for (
+
+            int i = 1; i <= n; i++) {
+            for (int j = 1; j < n; j = j * 2) {
+                // System.out.println("Hey - I'm busy looking at: " + i + " and " + j);
+                total++;
+            }
+        }
+        System.out.println("Total amount of times run: " + total);
+        System.out.println();
+    }
+
+    @Test
+    public void whenQuadraticComplexity_thenQuadraticRuntime() {
+        // Quadratic Time
+        System.out.println("**** Quadratic Time ****");
+        total = 0;
+        for (
+
+            int i = 1; i <= n; i++) {
+            for (int j = 1; j <= n; j++) {
+                // System.out.println("Hey - I'm busy looking at: " + i + " and " + j);
+                total++;
+            }
+        }
+        System.out.println("Total amount of times run: " + total);
+        System.out.println();
+    }
+
+    @Test
+    public void whenCubicComplexity_thenCubicRuntime() {
+        // Cubic Time
+        System.out.println("**** Cubic Time ****");
+        total = 0;
+        for (
+
+            int i = 1; i <= n; i++) {
+            for (int j = 1; j <= n; j++) {
+                for (int k = 1; k <= n; k++) {
+                    // System.out.println("Hey - I'm busy looking at: " + i + " and " + j + " and " + k);
+                    total++;
+                }
+            }
+        }
+        System.out.println("Total amount of times run: " + total);
+        System.out.println();
+    }
+
+    @Test
+    public void whenExponentialComplexity_thenExponentialRuntime() {
+        // Exponential Time
+        System.out.println("**** Exponential Time ****");
+        total = 0;
+        for (
+
+            int i = 1; i <= Math.pow(2, n); i++) {
+            // System.out.println("Hey - I'm busy looking at: " + i);
+            total++;
+        }
+        System.out.println("Total amount of times run: " + total);
+        System.out.println();
+    }
+
+    @Test
+    public void whenFactorialComplexity_thenFactorialRuntime() {
+        // Factorial Time
+        System.out.println("**** Factorial Time ****");
+        total = 0;
+        for (
+
+            int i = 1; i <=
+
+            factorial(n); i++) {
+            // System.out.println("Hey - I'm busy looking at: " + i);
+            total++;
+        }
+        System.out.println("Total amount of times run: " + total);
+    }
+
+    static int factorial(int n) {
+        if (n == 0 || n == 1)
+            return 1;
+        else
+            return n * factorial(n - 1);
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/checksortedlist/SortedListCheckerUnitTest.java

@@ -0,0 +1,106 @@
+package com.baeldung.algorithms.checksortedlist;
+
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingComparators;
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingIterativeApproach;
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingOrderingClass;
+import static com.baeldung.algorithms.checksortedlist.SortedListChecker.checkIfSortedUsingRecursion;
+import static java.util.Arrays.asList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class SortedListCheckerUnitTest {
+
+    private List<String> sortedListOfString;
+    private List<String> unsortedListOfString;
+    private List<String> singletonList;
+
+    private List<Employee> employeesSortedByName;
+    private List<Employee> employeesNotSortedByName;
+
+    @Before
+    public void setUp() {
+        sortedListOfString = asList("Canada", "HK", "LA", "NJ", "NY");
+        unsortedListOfString = asList("LA", "HK", "NJ", "NY", "Canada");
+        singletonList = Collections.singletonList("NY");
+
+        employeesSortedByName = asList(new Employee(1L, "John"), new Employee(2L, "Kevin"), new Employee(3L, "Mike"));
+        employeesNotSortedByName = asList(new Employee(1L, "Kevin"), new Employee(2L, "John"), new Employee(3L, "Mike"));
+    }
+
+    @Test
+    public void givenSortedList_whenUsingIterativeApproach_thenReturnTrue() {
+        assertThat(checkIfSortedUsingIterativeApproach(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenSingleElementList_whenUsingIterativeApproach_thenReturnTrue() {
+        assertThat(checkIfSortedUsingIterativeApproach(singletonList)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingIterativeApproach_thenReturnFalse() {
+        assertThat(checkIfSortedUsingIterativeApproach(unsortedListOfString)).isFalse();
+    }
+
+    @Test
+    public void givenSortedListOfEmployees_whenUsingIterativeApproach_thenReturnTrue() {
+        assertThat(checkIfSortedUsingIterativeApproach(employeesSortedByName, Comparator.comparing(Employee::getName))).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedListOfEmployees_whenUsingIterativeApproach_thenReturnFalse() {
+        assertThat(checkIfSortedUsingIterativeApproach(employeesNotSortedByName, Comparator.comparing(Employee::getName))).isFalse();
+    }
+
+    @Test
+    public void givenSortedList_whenUsingRecursion_thenReturnTrue() {
+        assertThat(checkIfSortedUsingRecursion(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenSingleElementList_whenUsingRecursion_thenReturnTrue() {
+        assertThat(checkIfSortedUsingRecursion(singletonList)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingRecursion_thenReturnFalse() {
+        assertThat(checkIfSortedUsingRecursion(unsortedListOfString)).isFalse();
+    }
+
+    @Test
+    public void givenSortedList_whenUsingGuavaOrdering_thenReturnTrue() {
+        assertThat(checkIfSortedUsingOrderingClass(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingGuavaOrdering_thenReturnFalse() {
+        assertThat(checkIfSortedUsingOrderingClass(unsortedListOfString)).isFalse();
+    }
+
+    @Test
+    public void givenSortedListOfEmployees_whenUsingGuavaOrdering_thenReturnTrue() {
+        assertThat(checkIfSortedUsingOrderingClass(employeesSortedByName, Comparator.comparing(Employee::getName))).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedListOfEmployees_whenUsingGuavaOrdering_thenReturnFalse() {
+        assertThat(checkIfSortedUsingOrderingClass(employeesNotSortedByName, Comparator.comparing(Employee::getName))).isFalse();
+    }
+
+    @Test
+    public void givenSortedList_whenUsingGuavaComparators_thenReturnTrue() {
+        assertThat(checkIfSortedUsingComparators(sortedListOfString)).isTrue();
+    }
+
+    @Test
+    public void givenUnsortedList_whenUsingGuavaComparators_thenReturnFalse() {
+        assertThat(checkIfSortedUsingComparators(unsortedListOfString)).isFalse();
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/enumstatemachine/LeaveRequestStateUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.algorithms.enumstatemachine;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class LeaveRequestStateUnitTest {
+
+    @Test
+    public void givenLeaveRequest_whenStateEscalated_thenResponsibleIsTeamLeader() {
+        LeaveRequestState state = LeaveRequestState.Escalated;
+
+        assertEquals(state.responsiblePerson(), "Team Leader");
+    }
+
+
+    @Test
+    public void givenLeaveRequest_whenStateApproved_thenResponsibleIsDepartmentManager() {
+        LeaveRequestState state = LeaveRequestState.Approved;
+
+        assertEquals(state.responsiblePerson(), "Department Manager");
+    }
+
+    @Test
+    public void givenLeaveRequest_whenNextStateIsCalled_thenStateIsChanged() {
+        LeaveRequestState state = LeaveRequestState.Submitted;
+
+        state = state.nextState();
+        assertEquals(state, LeaveRequestState.Escalated);
+
+        state = state.nextState();
+        assertEquals(state, LeaveRequestState.Approved);
+
+        state = state.nextState();
+        assertEquals(state, LeaveRequestState.Approved);
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/graphcycledetection/GraphCycleDetectionUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.algorithms.graphcycledetection;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+import com.baeldung.algorithms.graphcycledetection.domain.Graph;
+import com.baeldung.algorithms.graphcycledetection.domain.Vertex;
+
+public class GraphCycleDetectionUnitTest {
+
+    @Test
+    public void givenGraph_whenCycleExists_thenReturnTrue() {
+
+        Vertex vertexA = new Vertex("A");
+        Vertex vertexB = new Vertex("B");
+        Vertex vertexC = new Vertex("C");
+        Vertex vertexD = new Vertex("D");
+
+        Graph graph = new Graph();
+        graph.addVertex(vertexA);
+        graph.addVertex(vertexB);
+        graph.addVertex(vertexC);
+        graph.addVertex(vertexD);
+
+        graph.addEdge(vertexA, vertexB);
+        graph.addEdge(vertexB, vertexC);
+        graph.addEdge(vertexC, vertexA);
+        graph.addEdge(vertexD, vertexC);
+
+        assertTrue(graph.hasCycle());
+    }
+
+    @Test
+    public void givenGraph_whenNoCycleExists_thenReturnFalse() {
+
+        Vertex vertexA = new Vertex("A");
+        Vertex vertexB = new Vertex("B");
+        Vertex vertexC = new Vertex("C");
+        Vertex vertexD = new Vertex("D");
+
+        Graph graph = new Graph();
+        graph.addVertex(vertexA);
+        graph.addVertex(vertexB);
+        graph.addVertex(vertexC);
+        graph.addVertex(vertexD);
+
+        graph.addEdge(vertexA, vertexB);
+        graph.addEdge(vertexB, vertexC);
+        graph.addEdge(vertexA, vertexC);
+        graph.addEdge(vertexD, vertexC);
+
+        assertFalse(graph.hasCycle());
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/printtriangles/PrintTriangleExamplesUnitTest.java

@@ -0,0 +1,101 @@
+package com.baeldung.algorithms.printtriangles;
+
+import junitparams.JUnitParamsRunner;
+import junitparams.Parameters;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(JUnitParamsRunner.class)
+public class PrintTriangleExamplesUnitTest {
+
+    private static Object[][] rightTriangles() {
+        String expected0 = "";
+        
+        String expected2 = "*" + System.lineSeparator() 
+                         + "**" + System.lineSeparator();
+        
+        String expected5 = "*" + System.lineSeparator() 
+                         + "**" + System.lineSeparator()
+                         + "***" + System.lineSeparator()
+                         + "****" + System.lineSeparator()
+                         + "*****" + System.lineSeparator();
+        
+        String expected7 = "*" + System.lineSeparator() 
+                         + "**" + System.lineSeparator()
+                         + "***" + System.lineSeparator()
+                         + "****" + System.lineSeparator()
+                         + "*****" + System.lineSeparator()
+                         + "******" + System.lineSeparator()
+                         + "*******" + System.lineSeparator();
+        
+        return new Object[][] {
+            { 0, expected0 },
+            { 2, expected2 },
+            { 5, expected5 },
+            { 7, expected7 }
+        };
+    }
+
+    @Test
+    @Parameters(method = "rightTriangles")
+    public void whenPrintARightTriangleIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printARightTriangle(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+    
+    private static Object[][] isoscelesTriangles() {
+        String expected0 = ""; 
+        
+        String expected2 = " *" + System.lineSeparator() 
+                         + "***" + System.lineSeparator();
+        
+        String expected5 = "    *" + System.lineSeparator() 
+                         + "   ***" + System.lineSeparator()
+                         + "  *****" + System.lineSeparator()
+                         + " *******" + System.lineSeparator()
+                         + "*********" + System.lineSeparator();
+        
+        String expected7 = "      *" + System.lineSeparator() 
+                         + "     ***" + System.lineSeparator()
+                         + "    *****" + System.lineSeparator()
+                         + "   *******" + System.lineSeparator()
+                         + "  *********" + System.lineSeparator()
+                         + " ***********" + System.lineSeparator()
+                         + "*************" + System.lineSeparator();
+        
+        return new Object[][] {
+            { 0, expected0 },
+            { 2, expected2 },
+            { 5, expected5 },
+            { 7, expected7 }
+        };
+    }
+
+    @Test
+    @Parameters(method = "isoscelesTriangles")
+    public void whenPrintAnIsoscelesTriangleIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printAnIsoscelesTriangle(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    @Parameters(method = "isoscelesTriangles")
+    public void whenPrintAnIsoscelesTriangleUsingStringUtilsIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printAnIsoscelesTriangleUsingStringUtils(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+    
+    @Test
+    @Parameters(method = "isoscelesTriangles")
+    public void whenPrintAnIsoscelesTriangleUsingSubstringIsCalled_ThenTheCorrectStringIsReturned(int nrOfRows, String expected) {
+        String actual = PrintTriangleExamples.printAnIsoscelesTriangleUsingSubstring(nrOfRows);
+
+        assertEquals(expected, actual);
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/romannumerals/RomanArabicConverterUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.algorithms.romannumerals;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class RomanArabicConverterUnitTest {
+
+    @Test
+    public void given2018Roman_WhenConvertingToArabic_ThenReturn2018() {
+
+        String roman2018 = "MMXVIII";
+
+        int result = RomanArabicConverter.romanToArabic(roman2018);
+
+        assertThat(result).isEqualTo(2018);
+    }
+
+    @Test
+    public void given1999Arabic_WhenConvertingToRoman_ThenReturnMCMXCIX() {
+
+        int arabic1999 = 1999;
+
+        String result = RomanArabicConverter.arabicToRoman(arabic1999);
+
+        assertThat(result).isEqualTo("MCMXCIX");
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/twopointertechnique/LinkedListFindMiddleUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class LinkedListFindMiddleUnitTest {
+
+    LinkedListFindMiddle linkedListFindMiddle = new LinkedListFindMiddle();
+
+    @Test
+    public void givenLinkedListOfMyNodes_whenLinkedListFindMiddle_thenCorrect() {
+
+        MyNode<String> head = createNodesList(8);
+
+        assertThat(linkedListFindMiddle.findMiddle(head)).isEqualTo("4");
+
+        head = createNodesList(9);
+
+        assertThat(linkedListFindMiddle.findMiddle(head)).isEqualTo("5");
+    }
+
+    private static MyNode<String> createNodesList(int n) {
+
+        MyNode<String> head = new MyNode<String>("1");
+        MyNode<String> current = head;
+
+        for (int i = 2; i <= n; i++) {
+            MyNode<String> newNode = new MyNode<String>(String.valueOf(i));
+            current.setNext(newNode);
+            current = newNode;
+        }
+
+        return head;
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/twopointertechnique/RotateArrayUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class RotateArrayUnitTest {
+
+    private RotateArray rotateArray = new RotateArray();
+
+    private int[] inputArray;
+
+    private int step;
+
+    @Test
+    public void givenAnArrayOfIntegers_whenRotateKsteps_thenCorrect() {
+
+        inputArray = new int[] { 1, 2, 3, 4, 5, 6, 7 };
+        step = 4;
+
+        rotateArray.rotate(inputArray, step);
+
+        assertThat(inputArray).containsExactly(new int[] { 4, 5, 6, 7, 1, 2, 3 });
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/twopointertechnique/TwoSumUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.algorithms.twopointertechnique;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class TwoSumUnitTest {
+
+    private TwoSum twoSum = new TwoSum();
+
+    private int[] sortedArray;
+
+    private int targetValue;
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSumSlow_thenPairExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 12;
+
+        assertTrue(twoSum.twoSumSlow(sortedArray, targetValue));
+    }
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSumSlow_thenPairDoesNotExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 20;
+
+        assertFalse(twoSum.twoSumSlow(sortedArray, targetValue));
+    }
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSum_thenPairExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 12;
+
+        assertTrue(twoSum.twoSum(sortedArray, targetValue));
+    }
+
+    @Test
+    public void givenASortedArrayOfIntegers_whenTwoSum_thenPairDoesNotExists() {
+
+        sortedArray = new int[] { 0, 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 9 };
+
+        targetValue = 20;
+
+        assertFalse(twoSum.twoSum(sortedArray, targetValue));
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/counter/CounterStatistics.java

@@ -0,0 +1,61 @@
+package com.baeldung.counter;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Random;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Mode;
+
+import com.baeldung.counter.CounterUtil.MutableInteger;
+
+@Fork(value = 1, warmups = 3)
+@BenchmarkMode(Mode.All)
+public class CounterStatistics {
+
+    private static final Map<String, Integer> counterMap = new HashMap<>();
+    private static final Map<String, MutableInteger> counterWithMutableIntMap = new HashMap<>();
+    private static final Map<String, int[]> counterWithIntArrayMap = new HashMap<>();
+    private static final Map<String, Long> counterWithLongWrapperMap = new HashMap<>();
+    private static final Map<String, Long> counterWithLongWrapperStreamMap = new HashMap<>();
+    
+    static {
+        CounterUtil.COUNTRY_NAMES = new String[10000];
+        final String prefix = "NewString"; 
+        Random random = new Random();
+        for (int i=0; i<10000; i++) {
+            CounterUtil.COUNTRY_NAMES[i] = new String(prefix + random.nextInt(1000));
+        }
+    }
+
+  @Benchmark
+    public void wrapperAsCounter() {
+        CounterUtil.counterWithWrapperObject(counterMap);
+    }
+
+    @Benchmark
+    public void lambdaExpressionWithWrapper() {
+        CounterUtil.counterWithLambdaAndWrapper(counterWithLongWrapperMap);
+    }
+    
+    @Benchmark
+    public void parallelStreamWithWrapper() {
+        CounterUtil.counterWithParallelStreamAndWrapper(counterWithLongWrapperStreamMap);
+    }
+
+    @Benchmark
+    public void mutableIntegerAsCounter() {
+        CounterUtil.counterWithMutableInteger(counterWithMutableIntMap);
+    }
+
+    @Benchmark
+    public void primitiveArrayAsCounter() {
+        CounterUtil.counterWithPrimitiveArray(counterWithIntArrayMap);
+    }
+
+    public static void main(String[] args) throws Exception {
+        org.openjdk.jmh.Main.main(args);
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/counter/CounterUnitTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.counter;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.Assert.*;
+
+import org.junit.Test;
+
+import com.baeldung.counter.CounterUtil.MutableInteger;
+
+public class CounterUnitTest {
+
+    @Test
+    public void whenMapWithWrapperAsCounter_runsSuccessfully() {
+        Map<String, Integer> counterMap = new HashMap<>();
+        CounterUtil.counterWithWrapperObject(counterMap);
+
+        assertEquals(3, counterMap.get("China")
+            .intValue());
+        assertEquals(2, counterMap.get("India")
+            .intValue());
+    }
+
+    @Test
+    public void whenMapWithLambdaAndWrapperCounter_runsSuccessfully() {
+        Map<String, Long> counterMap = new HashMap<>();
+        CounterUtil.counterWithLambdaAndWrapper(counterMap);
+
+        assertEquals(3l, counterMap.get("China")
+            .longValue());
+        assertEquals(2l, counterMap.get("India")
+            .longValue());
+    }
+
+    @Test
+    public void whenMapWithMutableIntegerCounter_runsSuccessfully() {
+        Map<String, MutableInteger> counterMap = new HashMap<>();
+        CounterUtil.counterWithMutableInteger(counterMap);
+        assertEquals(3, counterMap.get("China")
+            .getCount());
+        assertEquals(2, counterMap.get("India")
+            .getCount());
+    }
+
+    @Test
+    public void whenMapWithPrimitiveArray_runsSuccessfully() {
+        Map<String, int[]> counterMap = new HashMap<>();
+        CounterUtil.counterWithPrimitiveArray(counterMap);
+        assertEquals(3, counterMap.get("China")[0]);
+        assertEquals(2, counterMap.get("India")[0]);
+    }
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/counter/CounterUtil.java

@@ -0,0 +1,57 @@
+package com.baeldung.counter;
+
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class CounterUtil {
+
+    public static String[] COUNTRY_NAMES = { "China", "Australia", "India", "USA", "USSR", "UK", "China", "France", "Poland", "Austria", "India", "USA", "Egypt", "China" };
+
+    public static void counterWithWrapperObject(Map<String, Integer> counterMap) {
+        for (String country : COUNTRY_NAMES) {
+            counterMap.compute(country, (k, v) -> v == null ? 1 : v + 1);
+        }
+    }
+
+    public static void counterWithLambdaAndWrapper(Map<String, Long> counterMap) {
+        Stream.of(COUNTRY_NAMES)
+            .collect(Collectors.groupingBy(k -> k, () -> counterMap, Collectors.counting()));
+    }
+
+    public static void counterWithParallelStreamAndWrapper(Map<String, Long> counterMap) {
+        Stream.of(COUNTRY_NAMES)
+            .parallel()
+            .collect(Collectors.groupingBy(k -> k, () -> counterMap, Collectors.counting()));
+    }
+
+    public static class MutableInteger {
+        int count;
+
+        public MutableInteger(int count) {
+            this.count = count;
+        }
+
+        public void increment() {
+            this.count++;
+        }
+
+        public int getCount() {
+            return this.count;
+        }
+    }
+
+    public static void counterWithMutableInteger(Map<String, MutableInteger> counterMap) {
+        for (String country : COUNTRY_NAMES) {
+            counterMap.compute(country, (k, v) -> v == null ? new MutableInteger(0) : v)
+                .increment();
+        }
+    }
+
+    public static void counterWithPrimitiveArray(Map<String, int[]> counterMap) {
+        for (String country : COUNTRY_NAMES) {
+            counterMap.compute(country, (k, v) -> v == null ? new int[] { 0 } : v)[0]++;
+        }
+    }
+
+}

algorithms-modules/algorithms-miscellaneous-3/src/test/java/com/baeldung/folding/FoldingHashUnitTest.java

@@ -0,0 +1,54 @@
+package com.baeldung.folding;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class FoldingHashUnitTest {
+
+    @Test
+    public void givenStringJavaLanguage_whenSize2Capacity100000_then48933() throws Exception {
+        final FoldingHash hasher = new FoldingHash();
+        final int value = hasher.hash("Java language", 2, 100_000);
+        assertEquals(value, 48933);
+    }
+
+    @Test
+    public void givenStringVaJaLanguage_whenSize2Capacity100000_thenSameAsJavaLanguage() throws Exception {
+        final FoldingHash hasher = new FoldingHash();
+        final int java = hasher.hash("Java language", 2, 100_000);
+        final int vaja = hasher.hash("vaJa language", 2, 100_000);
+        assertTrue(java == vaja);
+    }
+
+    @Test
+    public void givenSingleElementArray_whenOffset0Size2_thenSingleElement() throws Exception {
+        final FoldingHash hasher = new FoldingHash();
+        final int[] value = hasher.extract(new int[] { 5 }, 0, 2);
+        assertArrayEquals(new int[] { 5 }, value);
+    }
+
+    @Test
+    public void givenFiveElementArray_whenOffset0Size3_thenFirstThreeElements() throws Exception {
+        final FoldingHash hasher = new FoldingHash();
+        final int[] value = hasher.extract(new int[] { 1, 2, 3, 4, 5 }, 0, 3);
+        assertArrayEquals(new int[] { 1, 2, 3 }, value);
+    }
+
+    @Test
+    public void givenFiveElementArray_whenOffset1Size2_thenTwoElements() throws Exception {
+        final FoldingHash hasher = new FoldingHash();
+        final int[] value = hasher.extract(new int[] { 1, 2, 3, 4, 5 }, 1, 2);
+        assertArrayEquals(new int[] { 2, 3 }, value);
+    }
+
+    @Test
+    public void givenFiveElementArray_whenOffset2SizeTooBig_thenElementsToTheEnd() throws Exception {
+        final FoldingHash hasher = new FoldingHash();
+        final int[] value = hasher.extract(new int[] { 1, 2, 3, 4, 5 }, 2, 2000);
+        assertArrayEquals(new int[] { 3, 4, 5 }, value);
+    }
+
+}