Question:

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example:

  1. Input: "A man, a plan, a canal: Panama"
  2. Output: true
  1. Input: "race a car"
  2. Output: false

Solution:

  1. /**
  2.  * @param {string} s
  3.  * @return {boolean}
  4.  */
  5. var isPalindrome = function(s) {
  6.   if(!s)return true;
  7.   const regex = /[a-zA-Z0-9]+?/gi;
  8.   let str = s.match(regex);
  9.   if(!str) return true;
  10.   let len = str.length;
  11.   if(len === 1) return true;
  13.   for (let i = 0; i < Math.floor(len / 2); i++) {
  14.     if (str[i].toLowerCase() === str[len-i-1].toLowerCase()) continue;
  15.     return false;
  16.   }
  18.   return true;
  19. };

Runtime: 80 ms, faster than 39.01% of JavaScript online submissions for Valid Palindrome.