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

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);
+    }
+
+}