1 class Solution { 2 public: 3     /** 4      * @param s A string 5      * @return Whether the string is a valid palindrome 6      */ 7     bool isPalindrome(string& s) { 8         // Write your code here 9         int left = 0, right = s.length() - 1;10         while (left < right) {11             while (left < right && !isdigit(s[left]) && !isLetter(s[left]))12                 left++;13             if (left == right) break;14             while (right > left && !isdigit(s[right]) && !isLetter(s[right]))15                 right--;16             if (right == left) break;17             if (!match(s[left++], s[right--])) return false;18         }19         return true;20     }21 private:22     bool isLetter(char s) {23         return (s >= 'A' && s <= 'Z') || (s >= 'a' && s <= 'z');24     }25     bool match(char s, char t) {26         if (isLetter(s) && isLetter(t))27             return (s == t) || (s - t == 32) || (t - s == 32);28         return s == t;29     }30 };