merge: Add new IsPalindrome implementation (TheAlgorithms#1046)

HereBeAndre · web-flow · commit 6b06b3a37f1a · 2022-06-16T22:28:59.000+05:30
diff --git a/String/IsPalindrome.js b/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
+}
diff --git a/String/test/IsPalindrome.test.js b/String/test/IsPalindrome.test.js
@@ -0,0 +1,33 @@
+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()
+  })
+})
