LeetCode - 125. Valid Palindrome

class Solution {
public:
    bool isPalindrome(string s) {
        int l=0, r=s.size()-1;
        while(l<r){
            while(l<r && !isalnum(s[l])) l++;
            while(l<r && !isalnum(s[r])) r--;
            if(tolower(s[l++])!=tolower(s[r--])){
                return false;
            }
        }
        return true;
    }
};