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：

 1 class Solution {
 2 public:
 3     bool isPalindrome(string s) {
 4         if(!s.empty() && s.front() == ‘ ‘)
 5             s.erase(0, 1);
 6         if(!s.empty() && s.back() == ‘ ‘)
 7             s.pop_back();
 8
 9         bool ret = true;
10         int sz = s.size();
11         if(sz == 0)
12             return true;
13
14         int i = 0;
15         int j = sz - 1;
16         while(i < j)
17         {
18             while(i < sz && !isalnum(s[i]))
19                 i++;
20             while(j > -1 && !isalnum(s[j]))
21                 j--;
22             if(i < sz && j > -1 && s[i] != s[j])
23             {
24                 if(tolower(s[i]) != tolower(s[j]))
25                 {
26                     ret = false;
27                     break;
28                 }
29             }
30             i++;
31             j--;
32         }
33
34         return ret;
35     }
36 };