leetcode-Valid Palindrome

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.

 

class Solution {
public:
    bool isPalindrome(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        //空串直接认为是回文
        if (s.empty())
        {
            return true;
        }
        //对字符串进行处理,过滤掉不需要处理的字符
        string newS;
        for (string::size_type i = 0; i < s.size(); ++i)
        {
            if (isdigit(s[i]) || isalpha(s[i]))
            {
                newS.push_back(s[i]);
            }
        }
        //过滤后没有可供处理的字符，认为是回文
        if (newS.empty())
        {
            return true;
        }
        string::size_type first;
        string::size_type last;
        first = 0;
        last = newS.size() - 1;
        while (first < last)
        {
            if ((0 != newS[first] - newS[last]) && 32 != abs(newS[first] - newS[last]))
            {
                break;
            }
            ++first;
            --last;
        }
        
        return (first >= last)?true:false;
    }
};