merge: Add new IsPalindrome implementation (TheAlgorithms#1046)

Author: HereBeAndre

String/IsPalindrome.js

@@ -0,0 +1,36 @@
+/**
+ * @function isPalindromeIterative
+ * @description isPalindromeIterative function checks whether the provided input is palindrome or not
+ * @param {String | Number} x - The input to check
+ * @return {boolean} - Input is palindrome or not
+ * @see [Palindrome](https://en.wikipedia.org/wiki/Palindrome)
+ */
+
+/*
+ * Big-O Analysis
+ * Time Complexity
+ - O(N) on average and worst case scenario as input is traversed in linear fashion
+ - O(N) on best case scenario, even when input has length of 1, because toString() method takes O(N)
+ * Space Complexity
+ - O(1)
+*/
+
+export function isPalindromeIterative (x) {
+ if (typeof x !== 'string' && typeof x !== 'number') {
+ throw new TypeError('Input must be a string or a number')
+ }
+
+ // Convert x to string whether it's number or string
+ const string = x.toString()
+ const length = string.length
+
+ if (length === 1) return true
+
+ // Apply two pointers technique to compare first and last elements on each iteration
+ for (let start = 0, end = length - 1; start < end; start++, end--) {
+ // Early return if compared items are different, input is not a palindrome
+ if (string[start] !== string[end]) return false
+ }
+ // If early return in condition inside for loop is not reached, then input is palindrome
+ return true
+}

String/test/IsPalindrome.test.js

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+import { isPalindromeIterative } from '../IsPalindrome'
+
+describe('isPalindrome', () => {
+ it('expects to return true with empty string', () => {
+ expect(isPalindromeIterative('')).toEqual(true)
+ })
+
+ it('expects to return true when length of input is 1', () => {
+ const numberInput = 6
+ const stringInput = 'a'
+ expect(isPalindromeIterative(numberInput)).toEqual(true)
+ expect(isPalindromeIterative(stringInput)).toEqual(true)
+ })
+
+ it('expects to return true when input is palindrome', () => {
+ expect(isPalindromeIterative(121)).toEqual(true)
+ expect(isPalindromeIterative('yooy')).toEqual(true)
+ expect(isPalindromeIterative('19noon91')).toEqual(true)
+ expect(isPalindromeIterative('!*tyyt*!')).toEqual(true)
+ })
+
+ it('expects to return false when input is not palindrome', () => {
+ expect(isPalindromeIterative('hello')).toEqual(false)
+ expect(isPalindromeIterative(189)).toEqual(false)
+ expect(isPalindromeIterative('!*98[!')).toEqual(false)
+ })
+
+ it('expects to throw error when input is not a string or a number', () => {
+ expect(() => isPalindromeIterative(undefined)).toThrowError()
+ expect(() => isPalindromeIterative({ key: 'val' })).toThrowError()
+ expect(() => isPalindromeIterative([])).toThrowError()
+ })
+})