[LeetCode 125] Valid Palindrome

 1 class Solution {
 2 public:
 3     bool isPalindrome(string s) {
 4         transform(s.begin(), s.end(), s.begin(), ::tolower);
 5         auto left = s.begin();
 6         auto right = prev(s.end());
 7         while(left < right) {
 8             if(!::isalnum(*left))
 9                 ++left;
10             else if(!::isalnum(*right))
11                 --right;
12             else if(*left != *right)
13                 return false;
14             else{
15                 ++left;
16                 --right;
17             }
18         }
19         return true;
20     }
21 };

1 transform(s.begin(), s.end(), s.begin(), ::tolower);