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(0, 1);
        if(!s.empty() && s.back() == ' ')
            s.pop_back();
        
        bool ret = true;
        int sz = s.size();
        if(sz == 0)
            return true;
        
        int i = 0;
        int j = sz - 1;
        while(i < j)
        {
            while(i < sz && !isalnum(s[i]))
                i++;
            while(j > -1 && !isalnum(s[j]))
                j--;
            if(i < sz && j > -1 && s[i] != s[j])
            {
                if(tolower(s[i]) != tolower(s[j]))
                {
                    ret = false;
                    break;
                }
            }
            i++;
            j--;
        }
        
        return ret;
    }
};