LeetCode之“字符串”：Valid Palindrome

　　题目链接

　　题目要求：

　　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.

　　Note:
　　Have you consider that the string might be empty? This is a good question to ask during an interview.

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

　　程序如下：

 class Solution {
 public:
     bool isPalindrome(string s) {
         if(!s.empty() && s.front() == ' ')
             s.erase(, );
         if(!s.empty() && s.back() == ' ')
             s.pop_back();

         bool ret = true;
         int sz = s.size();
         if(sz == )
             return true;

         int i = ;
         int j = sz - ;
         while(i < j)
         {
             while(i < sz && !isalnum(s[i]))
                 i++;
             while(j > - && !isalnum(s[j]))
                 j--;
             if(i < sz && j > - && s[i] != s[j])
             {
                 if(tolower(s[i]) != tolower(s[j]))
                 {
                     ret = false;
                     break;
                 }
             }
             i++;
             j--;
         }

         return ret;
     }
 };