5 - 125. Valid Palindrome

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

var isPalindrome = function(s) {
    s = s.toLowerCase();
    
    let str = '';
    for (let i = 0; i <= s.length; i++) {
        if ((s[i] >= 0 && s[i] < 10) || (s[i] >= 'a' && s[i] < 'z')) {
             (s[i] !== ' ') && (str += s[i]);
        }
    }
    
    let flag = true;
    for (let i = 0; i < (str.length - 1)/2; i++) {
        if (str[i] !== str[str.length - 1 - i]) {
            flag = false;
            break;
        }
    }
    
    return flag;
};

in the case s[i] === ' ' the expression s[i] >= 0 returns true, so we need to filter it with expression s[i] !== ' '

another better approach

var isPalindrome = function(s) {
    let start = 0;
    let end = s.length - 1;
    
    while (start <= end) {
        let left = s.charCodeAt(start);
        let right = s.charCodeAt(end);
        
        if (!isLetter(left)) {
            start++;
            continue;
        }
        
        if (!isLetter(right)) {
            end--;
            continue;
        }
        
        if (toLowerCase(left) !== toLowerCase(right)) {
            return false;
        }
        
        start++;
        end--;
    }
    
    return true;
};

function isLetter(code) {
    if (((code >= 48) && (code <= 57))
    || ((code >= 65) && (code <= 90))
    || ((code >= 97) && (code <= 122))) {
        return true;
    }
    
    return false;
}

function toLowerCase(code) {
    if (code >= 65 && code <= 90) {
        return code + 32
    }
    
    return code;
}

I forgot to increase start and decrease end during each execute in the loop in the first time I submitted the code which leads to time limit exceeded

Don't forget to check if the code causes an infinite loop

we can use regex to remove non-alphanumeric

s = s.replace(/[^A-Za-z0-9]/g, '')

and we can use Array.every to instead of while

first convert string

let string = s.toLowerCase().replace(/[^a-z0-9]/g, "");

then filter the string

return string.split('').slice(0, Math.floor(string.length / 2)).every((letter, index) => letter === string[string.length - 1 - index])