Leetcode Valid Palindrome

class Solution {
public:
    bool isPalindrome(string s) {
        int left= 0 , right = s.length()-1;
        while(left <= right){
            while(left<=right && !isalnum(s[left])) left++;
            while(left<=right && !isalnum(s[right])) right--;
            if(left > right) break;
            if(isalpha(s[left]) && isalpha(s[right]) && tolower(s[left]) == tolower(s[right])){
                left++;
                right--;
            }
            else if(isdigit(s[left])&& isdigit(s[right]) && s[left] == s[right]){
                left++;
                right--;
            }
            else break;
        }
        if(left <= right) return false;
        else return true;
    }
};