diff --git a/algorithms/src/main/java/com/baeldung/algorithms/RunAlgorithm.java b/algorithms/src/main/java/com/baeldung/algorithms/RunAlgorithm.java index 6ab7dbb4e5..c82883425d 100644 --- a/algorithms/src/main/java/com/baeldung/algorithms/RunAlgorithm.java +++ b/algorithms/src/main/java/com/baeldung/algorithms/RunAlgorithm.java @@ -6,6 +6,7 @@ import com.baeldung.algorithms.ga.annealing.SimulatedAnnealing; import com.baeldung.algorithms.ga.ant_colony.AntColonyOptimization; import com.baeldung.algorithms.ga.binary.SimpleGeneticAlgorithm; import com.baeldung.algorithms.slope_one.SlopeOne; +import com.baeldung.algorithms.pairsaddupnumber.FindPairs; public class RunAlgorithm { @@ -17,6 +18,7 @@ public class RunAlgorithm { System.out.println("3 - Simple Genetic Algorithm"); System.out.println("4 - Ant Colony"); System.out.println("5 - Dijkstra"); + System.out.println("6 - All pairs in an array that add up to a given sum"); int decision = in.nextInt(); switch (decision) { case 1: @@ -37,6 +39,12 @@ public class RunAlgorithm { case 5: System.out.println("Please run the DijkstraAlgorithmTest."); break; + case 6: + final FindPairs findPairs = new FindPairs(); + final int[] input = {1, 4, 3, 2, 1, 4, 4, 3, 3}; + final int sum = 6; + findPairs.execute(input, sum); + break; default: System.out.println("Unknown option"); break; diff --git a/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/DifferentPairs.java b/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/DifferentPairs.java new file mode 100644 index 0000000000..e86e1d5a22 --- /dev/null +++ b/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/DifferentPairs.java @@ -0,0 +1,72 @@ +package com.baeldung.algorithms.pairsaddupnumber; + + +import java.util.ArrayList; +import java.util.HashMap; +import java.util.List; +import java.util.Map; +import java.util.stream.IntStream; + +/** + * Find all different pairs of numbers in an array that add up to a given sum - Complexity O(n) + */ +public class DifferentPairs { + + /** + * Show all different pairs using traditional "for" loop + * + * @param input - number's array + * @param sum - given sum + * @return - number's array with all existing pairs. This list will contain just one pair's element because + * the other one can be calculated with SUM - element_1 = element_2 + */ + public static List findPairsWithForLoop(int[] input, int sum) { + final List allDifferentPairs = new ArrayList<>(); + // Aux. hash map + final Map pairs = new HashMap(); + for (int i : input) { + if (pairs.containsKey(i)) { + if (pairs.get(i) != null) { + // Add pair to returned list + allDifferentPairs.add(i); + } + // Mark pair as added to prevent duplicates + pairs.put(sum - i, null); + } else if (!pairs.containsValue(i)) { + // Add pair to aux. hash map + pairs.put(sum - i, i); + } + } + return allDifferentPairs; + } + + /** + * Show all different pairs using Java 8 stream API + * + * @param input - number's array + * @param sum - given sum + * @return - number's array with all existing pairs. This list will contain just one pair's element because + * the other one can be calculated with SUM - element_1 = element_2 + */ + public static List findPairsWithStreamApi(int[] input, int sum) { + final List allDifferentPairs = new ArrayList<>(); + // Aux. hash map + final Map pairs = new HashMap(); + IntStream.range(0, input.length).forEach(i -> { + if (pairs.containsKey(input[i])) { + if (pairs.get(input[i]) != null) { + // Add pair to returned list + allDifferentPairs.add(input[i]); + } + // Mark pair as added to prevent duplicates + pairs.put(sum - input[i], null); + } else if (!pairs.containsValue(input[i])) { + // Add pair to aux. hash map + pairs.put(sum - input[i], input[i]); + } + } + ); + return allDifferentPairs; + } +} + diff --git a/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/ExistingPairs.java b/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/ExistingPairs.java new file mode 100644 index 0000000000..6b10c73bcf --- /dev/null +++ b/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/ExistingPairs.java @@ -0,0 +1,51 @@ +package com.baeldung.algorithms.pairsaddupnumber; + + +import java.util.ArrayList; +import java.util.List; +import java.util.stream.IntStream; + +/** + * Find all existing pairs of numbers in an array that add up to a given sum - Complexity O(n^2) "Brute force" + */ +public class ExistingPairs { + + /** + * Show all existing pairs using traditional "for" loop + * + * @param input - number's array + * @param sum - given sum + * @return - number's array with all existing pairs. This list will contain just one pair's element because + * the other one can be calculated with SUM - element_1 = element_2 + */ + public static List findPairsWithForLoop(int[] input, int sum) { + final List allExistingPairs = new ArrayList<>(); + for (int i = 0; i < input.length; i++) { + for (int j = 0; j < input.length; j++) { + if (j != i && (input[i] + input[j]) == sum) { + allExistingPairs.add(input[i]); + } + } + } + return allExistingPairs; + } + + /** + * Show all existing pairs using Java 8 stream API + * + * @param input - number's array + * @param sum - given sum + * @return - number's array with all existing pairs. This list will contain just one pair's element because + * the other one can be calculated with SUM - element_1 = element_2 + */ + public static List findPairsWithStreamApi(int[] input, int sum) { + final List allExistingPairs = new ArrayList<>(); + IntStream.range(0, input.length).forEach(i -> + IntStream.range(0, input.length) + .filter(j -> i != j && input[i] + input[j] == sum) + .forEach(j -> allExistingPairs.add(input[i])) + ); + return allExistingPairs; + } +} + diff --git a/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/FindPairs.java b/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/FindPairs.java new file mode 100644 index 0000000000..4b309332ae --- /dev/null +++ b/algorithms/src/main/java/com/baeldung/algorithms/pairsaddupnumber/FindPairs.java @@ -0,0 +1,74 @@ +package com.baeldung.algorithms.pairsaddupnumber; + +import java.util.ArrayList; +import java.util.List; +import java.util.stream.IntStream; + + +public class FindPairs { + + public void execute(int[] input, int sum) { + final StringBuilder inputArray = new StringBuilder(); + inputArray.append("{"); + IntStream.range(0, input.length).forEach(i -> inputArray.append(input[i] + ", ")); + inputArray.append("}"); + System.out.println(" Given number array: " + inputArray.toString()); + System.out.println(" Given sum: " + sum); + /* Call services */ + getDifferentPairs(input, sum); + getExistingPairs(input, sum); + } + + /** + * Print all existing pairs for the given inputs: input array & sum number + */ + private static void getExistingPairs(int[] input, int sum) { + List pairs = new ArrayList<>(); + System.out.println("~ All existing pairs ~"); + + /* Traditional FOR loop */ + // Call method + pairs = ExistingPairs.findPairsWithForLoop(input, sum); + // Create a pretty printing + final StringBuilder output1 = new StringBuilder(); + pairs.forEach((pair) -> output1.append("{" + pair + ", " + (sum - pair) + "}, ")); + // Print result + System.out.println("Traditional \"for\" loop: " + output1.toString().substring(0, output1.length() - 2)); + + /* Java 8 stream API */ + // Call the method + pairs = ExistingPairs.findPairsWithStreamApi(input, sum); + // Create a pretty printing + final StringBuilder output2 = new StringBuilder(); + pairs.forEach((pair) -> output2.append("{" + pair + ", " + (sum - pair) + "}, ")); + // Print result + System.out.println("Java 8 streams API: " + output2.toString().substring(0, output2.length() - 2)); + } + + /** + * Print all different pairs for the given inputs: input array & sum number + */ + private static void getDifferentPairs(int[] input, int sum) { + List pairs = new ArrayList<>(); + System.out.println("~ All different pairs ~"); + + /* Traditional FOR loop */ + // Call method + pairs = DifferentPairs.findPairsWithForLoop(input, sum); + // Create a pretty printing + final StringBuilder output3 = new StringBuilder(); + pairs.forEach((pair) -> output3.append("{" + pair + ", " + (sum - pair) + "}, ")); + // Print result + System.out.println("Traditional \"for\" loop: " + output3.toString().substring(0, output3.length() - 2)); + + /* Java 8 stream API */ + // Call method + pairs = DifferentPairs.findPairsWithStreamApi(input, sum); + // Create a pretty printing + final StringBuilder output4 = new StringBuilder(); + pairs.forEach((pair) -> output4.append("{" + pair + ", " + (sum - pair) + "}, ")); + // Print result + System.out.println("Java 8 streams API: " + output4.toString().substring(0, output4.length() - 2)); + } +} + diff --git a/algorithms/src/test/java/com/baeldung/algorithms/pairsaddupnumber/DifferentPairsUnitTest.java b/algorithms/src/test/java/com/baeldung/algorithms/pairsaddupnumber/DifferentPairsUnitTest.java new file mode 100644 index 0000000000..48fcfb871c --- /dev/null +++ b/algorithms/src/test/java/com/baeldung/algorithms/pairsaddupnumber/DifferentPairsUnitTest.java @@ -0,0 +1,39 @@ +package com.baeldung.algorithms.pairsaddupnumber; + +import org.junit.Test; + +import java.util.List; + +import static org.assertj.core.api.Assertions.assertThat; +import static org.junit.Assert.assertEquals; +import static org.junit.Assert.assertNotNull; + +public class DifferentPairsUnitTest { + + /* All different pairs */ + + @Test + public void whenTraditionalLoop_thenReturnAllDifferentPairs() { + /* Data */ + final int[] input = {2, 4, 3, 3, 8}; + final int sum = 6; + /* Call service */ + final List pairs = DifferentPairs.findPairsWithForLoop(input, sum); + /* Check results */ + assertThat(pairs).hasSize(2).contains(4,3).doesNotContain(8); + } + + @Test + public void whenStreamApi_thenReturnAllDifferentPairs() { + /* Data */ + final int[] input = {2, 4, 3, 3, 8}; + final int sum = 6; + /* Call service */ + final List pairs = DifferentPairs.findPairsWithStreamApi(input, sum); + /* Check results */ + assertNotNull(pairs); + assertEquals(pairs.size(),2); + assertEquals(pairs.get(0), new Integer(4)); + assertThat(pairs).hasSize(2).contains(4,3).doesNotContain(8); + } +} diff --git a/algorithms/src/test/java/com/baeldung/algorithms/pairsaddupnumber/ExistingPairsUnitTest.java b/algorithms/src/test/java/com/baeldung/algorithms/pairsaddupnumber/ExistingPairsUnitTest.java new file mode 100644 index 0000000000..ac6d6cc885 --- /dev/null +++ b/algorithms/src/test/java/com/baeldung/algorithms/pairsaddupnumber/ExistingPairsUnitTest.java @@ -0,0 +1,34 @@ +package com.baeldung.algorithms.pairsaddupnumber; + +import org.junit.Test; +import java.util.List; + +import static org.assertj.core.api.Assertions.assertThat; + + +public class ExistingPairsUnitTest { + + /* All existing pairs */ + + @Test + public void whenTraditionalLoop_thenReturnAllExistingPairs() { + /* Data */ + final int[] input = {2, 4, 3, 3, 8}; + final int sum = 6; + /* Call service */ + final List pairs = ExistingPairs.findPairsWithForLoop(input, sum); + /* Check results */ + assertThat(pairs).hasSize(4).contains(2,4,3,3).doesNotContain(8); + } + + @Test + public void whenStreamApi_thenReturnAllExistingPairs() { + /* Data */ + final int[] input = {2, 4, 3, 3, 8}; + final int sum = 6; + /* Call service */ + final List pairs = ExistingPairs.findPairsWithStreamApi(input, sum); + /* Check results */ + assertThat(pairs).hasSize(4).contains(2,4,3,3).doesNotContain(8); + } +}