LeetCode ：Valid Palindrome

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

For example,
“A man, a plan, a canal: Panama” is a palindrome.
“race a car” is not a palindrome.

class Solution {public:    bool isPalindrome(string s) {        int left = 0, right = s.size() - 1 ;        while (left < right) {            if (!isalnum(s[left])) ++left;            else if (!isalnum(s[right])) --right;            else if ((s[left] + 32 - 'a') %32 != (s[right] + 32 - 'a') % 32) return false;            else {                ++left; --right;            }        }        return true;    }};