diff --git a/DIRECTORY.md b/DIRECTORY.md index b880021a6ddb..1c1c010221a3 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -858,6 +858,7 @@ * [GenericHashMapUsingArrayListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/GenericHashMapUsingArrayListTest.java) * [GenericHashMapUsingArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/GenericHashMapUsingArrayTest.java) * [HashMapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/HashMapTest.java) + * [IntersectionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/IntersectionTest.java) * [LinearProbingHashMapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/LinearProbingHashMapTest.java) * [MajorityElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/MajorityElementTest.java) * [MapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/MapTest.java) diff --git a/src/main/java/com/thealgorithms/datastructures/hashmap/hashing/Intersection.java b/src/main/java/com/thealgorithms/datastructures/hashmap/hashing/Intersection.java index 54bd10de50fa..0e49218d6348 100644 --- a/src/main/java/com/thealgorithms/datastructures/hashmap/hashing/Intersection.java +++ b/src/main/java/com/thealgorithms/datastructures/hashmap/hashing/Intersection.java @@ -1,27 +1,57 @@ package com.thealgorithms.datastructures.hashmap.hashing; -/* - * this is algo which implies common mathematical set theory concept - * called intersection in which result is common values of both the sets - * here metaphor of sets is HashMap - */ - import java.util.ArrayList; import java.util.Collections; import java.util.HashMap; import java.util.List; import java.util.Map; +/** + * The {@code Intersection} class provides a method to compute the intersection of two integer arrays. + * The intersection is defined as the set of common elements present in both arrays. + *

+ * This class utilizes a HashMap to efficiently count occurrences of elements in the first array, + * allowing for an efficient lookup of common elements in the second array. + *

+ * + *

+ * Example: + * 

+ * int[] array1 = {1, 2, 2, 1};
+ * int[] array2 = {2, 2};
+ * List result = Intersection.intersection(array1, array2); // result will contain [2, 2]
+ *
+ *

+ * + *

+ * Note: The order of the returned list may vary since it depends on the order of elements + * in the input arrays. + *

+ */ public final class Intersection { + /** + * Computes the intersection of two integer arrays. + * Steps: + * 1. Count the occurrences of each element in the first array using a HashMap. + * 2. Iterate over the second array and check if the element is present in the HashMap. + * If it is, add it to the result list and decrement the count in the HashMap. + * 3. Return the result list containing the intersection of the two arrays. + * + * @param arr1 the first array of integers + * @param arr2 the second array of integers + * @return a list containing the intersection of the two arrays, or an empty list if either array is null or empty + */ public static List intersection(int[] arr1, int[] arr2) { if (arr1 == null || arr2 == null || arr1.length == 0 || arr2.length == 0) { return Collections.emptyList(); } + Map cnt = new HashMap<>(16); for (int v : arr1) { cnt.put(v, cnt.getOrDefault(v, 0) + 1); } + List res = new ArrayList<>(); for (int v : arr2) { if (cnt.containsKey(v) && cnt.get(v) > 0) { diff --git a/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/IntersectionTest.java b/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/IntersectionTest.java new file mode 100644 index 000000000000..df6d15fd9ba4 --- /dev/null +++ b/src/test/java/com/thealgorithms/datastructures/hashmap/hashing/IntersectionTest.java @@ -0,0 +1,76 @@ +package com.thealgorithms.datastructures.hashmap.hashing; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertTrue; + +import java.util.List; +import org.junit.jupiter.api.Test; + +public class IntersectionTest { + + @Test + void testBasicIntersection() { + int[] arr1 = {1, 2, 2, 1}; + int[] arr2 = {2, 2}; + List result = Intersection.intersection(arr1, arr2); + assertEquals(List.of(2, 2), result, "Intersection should return [2, 2]"); + } + + @Test + void testNoIntersection() { + int[] arr1 = {1, 2, 3}; + int[] arr2 = {4, 5, 6}; + List result = Intersection.intersection(arr1, arr2); + assertTrue(result.isEmpty(), "Intersection should be empty for disjoint sets"); + } + + @Test + void testEmptyArray() { + int[] arr1 = {}; + int[] arr2 = {1, 2, 3}; + List result = Intersection.intersection(arr1, arr2); + assertTrue(result.isEmpty(), "Intersection should be empty when first array is empty"); + + result = Intersection.intersection(arr2, arr1); + assertTrue(result.isEmpty(), "Intersection should be empty when second array is empty"); + } + + @Test + void testNullArray() { + int[] arr1 = null; + int[] arr2 = {1, 2, 3}; + List result = Intersection.intersection(arr1, arr2); + assertTrue(result.isEmpty(), "Intersection should be empty when first array is null"); + + result = Intersection.intersection(arr2, arr1); + assertTrue(result.isEmpty(), "Intersection should be empty when second array is null"); + } + + @Test + void testMultipleOccurrences() { + int[] arr1 = {5, 5, 5, 6}; + int[] arr2 = {5, 5, 6, 6, 6}; + List result = Intersection.intersection(arr1, arr2); + assertEquals(List.of(5, 5, 6), result, "Intersection should return [5, 5, 6]"); + } + + @Test + void testSameElements() { + int[] arr1 = {1, 1, 1}; + int[] arr2 = {1, 1, 1}; + List result = Intersection.intersection(arr1, arr2); + assertEquals(List.of(1, 1, 1), result, "Intersection should return [1, 1, 1] for same elements"); + } + + @Test + void testLargeArrays() { + int[] arr1 = new int[1000]; + int[] arr2 = new int[1000]; + for (int i = 0; i < 1000; i++) { + arr1[i] = i; + arr2[i] = i; + } + List result = Intersection.intersection(arr1, arr2); + assertEquals(1000, result.size(), "Intersection should return all elements for identical large arrays"); + } +}