[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
       string news;
       int n=s.size();
       int diff='a'-'A';
       for(int i=0 ; i<n ; i++){
           if(s[i]<='Z' && s[i]>='A')
                news.push_back(s[i]+diff);
            if(s[i]<='9' && s[i]>='0' || s[i]<='z' && s[i]>='a')
                news.push_back(s[i]);                
        }
        n=news.size();
        for(int i=0 ; i<n/2 ; i++){
            if(news[i]!=news[n-i-1])
                return false;
        }
        return true;
    }
};