Valid Palindrome

Problem Description

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.

Given a string s, return true if it is a palindrome, or false otherwise.

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 * 105
• s consists only of printable ASCII characters.

Solution (JavaScript)

/**
 * @param {string} s
 * @return {boolean}
 */
var isPalindrome = function(s) {
    const ss = s.replace(/[^A-Za-z0-9]/g, '').toLowerCase();
    for (let i = 0; i < ss.length/2; i++) {
        if(ss[i] !== ss[ss.length-1-i]) {
            return false;
        }
    }
    return true;
};