125. Valid Palindrome

time: O(n) ⇒ lowercase

space: O(1)

/**
 * @param {string} s
 * @return {boolean}
 */
var isPalindrome = function (str) {
    str = str.toLowerCase(); // n
    str = str.replace(/[^a-z0-9]/g, ''); // n
    console.log(str);

    let s = 0;
    let e = str.length - 1;

    while (s <= e) {
        if (str[s] !== str[e]) {
            return false;
        }

        s++;
        e--;
    }

    return true;
};

var isPalindrome = function (str) {
    str = str.toLowerCase(); // n

    let s = 0;
    let e = str.length - 1;

    while (s <= e) {
        if (!isAlphabetNumber(str[s])) {
            s++;
            continue;
        } else if (!isAlphabetNumber(str[e])) {
            e--;
            continue;
        } else {
            if (str[s] !== str[e]) {
                return false;
            }
            s++;
            e--;
        }
    }

    return true;
};

function isAlphabetNumber(c) {
    if ('0' <= c && c <= '9' ||
        'a'.charCodeAt() <= c.charCodeAt() && c.charCodeAt() <= 'z'.charCodeAt()) {
        return true;
    }

    return false;
}