LeetCode --- Valid Palindrome

 1 class Solution {
 2 public:
 3     bool isPalindrome(string s) {
 4         if (s.empty()) return true; // consider empty string as valid palindrome
 5         unsigned int len = s.size();
 6         unsigned int beg = 0, end = len - 1;
 7         while (beg < end) {
 8             while (beg <= end && !isdigit(s[beg]) && !isalpha(s[beg]))
 9                 beg++;
10             while (end >= beg && !isdigit(s[end]) && !isalpha(s[end]))
11                 end--;
12             //if (beg == end) return true;
13             if (beg >= end) return true;
14             if (isalpha(s[beg]) && isalpha(s[end])) {
15                 if (toupper(s[beg]) != toupper(s[end]))
16                     return false;
17             } else if (s[beg] != s[end]) {
18                 return false;
19             }
20             beg++;
21             end--;
22         }
23         
24         return true;
25     }
26 };