feat: add array intersection algorithm

Data-Structures/Array/Intersection.js

@@ -0,0 +1,21 @@
+/**
+ * @function intersection
+ * @description Returns a new array containing elements that exist
+ *   in both input arrays. Each element in the result is unique.
+ * @param {Array} arr1 - The first input array
+ * @param {Array} arr2 - The second input array
+ * @returns {Array} - Array of elements present in both arrays
+ * @see https://en.wikipedia.org/wiki/Intersection_(set_theory)
+ * @example intersection([1, 2, 3], [2, 3, 4]) => [2, 3]
+ * @example intersection([1, 2], [3, 4]) => []
+ * @example intersection([1, 1, 2], [1, 2, 2]) => [1, 2]
+ */
+const intersection = (arr1, arr2) => {
+  if (!Array.isArray(arr1) || !Array.isArray(arr2)) {
+    throw new TypeError('Both inputs must be arrays')
+  }
+  const set2 = new Set(arr2)
+  return [...new Set(arr1.filter((item) => set2.has(item)))]
+}
+
+export { intersection }

Data-Structures/Array/test/Intersection.test.js

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+import { intersection } from '../Intersection.js'
+
+describe('intersection', () => {
+  test('intersection([1,2,3],[2,3,4]) returns [2,3]', () => {
+    expect(intersection([1, 2, 3], [2, 3, 4])).toEqual([2, 3])
+  })
+
+  test('intersection([1,2],[3,4]) returns []', () => {
+    expect(intersection([1, 2], [3, 4])).toEqual([])
+  })
+
+  test('intersection([1,1,2],[1,2,2]) returns [1,2]', () => {
+    expect(intersection([1, 1, 2], [1, 2, 2])).toEqual([1, 2])
+  })
+
+  test('intersection with empty first array returns []', () => {
+    expect(intersection([], [1, 2, 3])).toEqual([])
+  })
+
+  test('intersection with empty second array returns []', () => {
+    expect(intersection([1, 2, 3], [])).toEqual([])
+  })
+
+  test('intersection with identical arrays returns same values', () => {
+    expect(intersection([1, 2, 3], [1, 2, 3])).toEqual([1, 2, 3])
+  })
+
+  test('intersection works with strings', () => {
+    expect(intersection(['a', 'b', 'c'], ['b', 'c', 'd'])).toEqual(['b', 'c'])
+  })
+
+  test('intersection does not mutate original arrays', () => {
+    const arr1 = [1, 2, 3]
+    const arr2 = [2, 3, 4]
+    intersection(arr1, arr2)
+    expect(arr1).toEqual([1, 2, 3])
+    expect(arr2).toEqual([2, 3, 4])
+  })
+
+  test('throws TypeError for non-array first input', () => {
+    expect(() => intersection('123', [1, 2])).toThrow(TypeError)
+  })
+
+  test('throws TypeError for non-array second input', () => {
+    expect(() => intersection([1, 2], '123')).toThrow(TypeError)
+  })
+})