125. Valid Palindrome

Problem

https://leetcode.com/problems/valid-palindrome/

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

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

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

Solution

Just burn the candle at both ends.

/**
 * @param {string} s
 * @return {boolean}
 */
var isPalindrome = function(s) {
    if (typeof s !== 'string') { return false }
    // empty stiring
    if (!s) { return true }

    let ss = s.toLowerCase()
    let i = 0
    let j = ss.length - 1
    let alphanumChecker = /\w/

    while (i < j) {
        while (!alphanumChecker.test(ss[i])) {
            if (i >= j) { return true }
            i += 1
        }
        while (!alphanumChecker.test(ss[j])) {
            if (i >= j) { return true }
            j -= 1
        }
        if (ss[i++] !== ss[j--]) { return false }
    }

    return true
};