added an algo which finds unique element in an array (#1359)

* added an algo which finds unique element in an array

* fixed code style

* updated changes and add some explanations

* Delete package-lock.json

* Delete package.json

* added question link if anyone want to solve

* updated changes

* added package.json

* used JSDoc comment

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Co-authored-by: madhuredra <madhuredra.tiwari@zemosolabs.com>

Bit-Manipulation/UniqueElementInAnArray.js

@@ -0,0 +1,13 @@
+/**
+ * Finds the unique element in an array where all other elements are repeated twice.
+ *
+ * @param {number[]} arr - The input array of integers.
+ * @returns {number} The unique element.
+ *
+ * @example
+ * const arr = [1, 2, 1, 2, 3];
+ * const uniqueElement = findUniqueElement(arr); // Returns 3
+ */
+const findUniqueElement = (arr) => arr.reduce((acc, val) => acc ^ val, 0)
+
+export { findUniqueElement }

Bit-Manipulation/test/UniqueElementInAnArray.test.js

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+import { findUniqueElement } from '../UniqueElementInAnArray'
+
+describe('UniqueElementInAnArray', () => {
+  it.each([
+    [[1, 2, 1, 3, 3], 2],
+    [[1, 2, 3, 4, 5, 4, 3, 2, 1], 5]
+  ])('should return an unique element from an array', (arr, expected) => {
+    expect(findUniqueElement(arr)).toBe(expected)
+  })
+})