From 1bbca7ae71ea011548fc1ca72a630aaf5cb3127b Mon Sep 17 00:00:00 2001
From: sarthakgupta1907-cell <sarthakgupta1907@gmail.com>
Date: Fri, 6 Nov 2026 10:58:26 +0530
Subject: [PATCH] feat: add array difference algorithm

---
 Data-Structures/Array/Difference.js           | 21 +++++++++
 Data-Structures/Array/test/Difference.test.js | 47 +++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 Data-Structures/Array/Difference.js
 create mode 100644 Data-Structures/Array/test/Difference.test.js

diff --git a/Data-Structures/Array/Difference.js b/Data-Structures/Array/Difference.js
new file mode 100644
index 0000000000..9abcfd6329
--- /dev/null
+++ b/Data-Structures/Array/Difference.js
@@ -0,0 +1,21 @@
+/**
+ * @function difference
+ * @description Returns a new array with elements that are in the first
+ *   array but not in the second array.
+ * @param {Array} arr1 - The first input array
+ * @param {Array} arr2 - The second input array
+ * @returns {Array} - Array of elements in arr1 but not in arr2
+ * @see https://en.wikipedia.org/wiki/Complement_(set_theory)
+ * @example difference([1, 2, 3], [2, 3, 4]) => [1]
+ * @example difference([1, 2, 3], [1, 2, 3]) => []
+ * @example difference([1, 2, 3], []) => [1, 2, 3]
+ */
+const difference = (arr1, arr2) => {
+  if (!Array.isArray(arr1) || !Array.isArray(arr2)) {
+    throw new TypeError('Both inputs must be arrays')
+  }
+  const set2 = new Set(arr2)
+  return arr1.filter((item) => !set2.has(item))
+}
+
+export { difference }
diff --git a/Data-Structures/Array/test/Difference.test.js b/Data-Structures/Array/test/Difference.test.js
new file mode 100644
index 0000000000..a47de8165a
--- /dev/null
+++ b/Data-Structures/Array/test/Difference.test.js
@@ -0,0 +1,47 @@
+import { difference } from '../Difference.js'
+
+describe('difference', () => {
+  test('difference([1,2,3],[2,3,4]) returns [1]', () => {
+    expect(difference([1, 2, 3], [2, 3, 4])).toEqual([1])
+  })
+
+  test('difference([1,2,3],[1,2,3]) returns []', () => {
+    expect(difference([1, 2, 3], [1, 2, 3])).toEqual([])
+  })
+
+  test('difference([1,2,3],[]) returns [1,2,3]', () => {
+    expect(difference([1, 2, 3], [])).toEqual([1, 2, 3])
+  })
+
+  test('difference([],[1,2,3]) returns []', () => {
+    expect(difference([], [1, 2, 3])).toEqual([])
+  })
+
+  test('difference([1,2,3],[4,5,6]) returns [1,2,3]', () => {
+    expect(difference([1, 2, 3], [4, 5, 6])).toEqual([1, 2, 3])
+  })
+
+  test('difference works with strings', () => {
+    expect(difference(['a', 'b', 'c'], ['b', 'c', 'd'])).toEqual(['a'])
+  })
+
+  test('difference does not mutate original arrays', () => {
+    const arr1 = [1, 2, 3]
+    const arr2 = [2, 3, 4]
+    difference(arr1, arr2)
+    expect(arr1).toEqual([1, 2, 3])
+    expect(arr2).toEqual([2, 3, 4])
+  })
+
+  test('difference keeps duplicates from arr1 not in arr2', () => {
+    expect(difference([1, 1, 2, 3], [2, 3])).toEqual([1, 1])
+  })
+
+  test('throws TypeError for non-array first input', () => {
+    expect(() => difference('123', [1, 2])).toThrow(TypeError)
+  })
+
+  test('throws TypeError for non-array second input', () => {
+    expect(() => difference([1, 2], '123')).toThrow(TypeError)
+  })
+})