125. Valid Palindrome

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers

Two Pointers

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters. Since an empty string reads the same forward and backward, it is a palindrome.

Constraints:

1 <= s.length <= 2 * 10^5
s consists only of printable ASCII characters.

Approach

Solution

/**
 * @param {string} s
 * @return {boolean}
 */
var isPalindrome = function(s) {
  let normal = s.replace(/[^a-zA-Z0-9]/g, "").toLowerCase()    
  let i = 0, j = normal.length - 1;

  while (i < j) {
    if(normal[i] !== normal[j]) {
      return false;
    }
    i++;
    j--;
  }
  return true;
};