125. Valid Palindrome

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

Problem

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example 1:

Input: "A man, a plan, a canal: Panama"
Output: true

Example 2:

Input: "race a car"
Output: false

Constraints:

• s consists only of printable ASCII characters.

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

• #string