class Solution {
public:
    bool isPalindrome(string s) {
        // two point left and right
        // if meet not alpha or number, skip
        // compare s[left] and s[right]
        // if equal, continue
        // if not equal return false
        // if left == right, return true

        int left = 0, right = s.size() - 1;

        for(; left < right; left++, right--) {
            while(left < right && !isalnum(s[left])) {
                left++;
            }

            while(left < right && !isalnum(s[right])) {
                right--;
            }

            if(tolower(s[left]) != tolower(s[right])) {
                return false;
            }
        }

        return true;
    }
};