125. Valid Palindrome（LeetCode）

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) {
      if (s == "")
            return true;
        int len = s.size();
        transform(s.begin(), s.end(), s.begin(), ::tolower);
        string s1="";
        for (int i = 0; i < len; i++)
        {
            if (isalnum(s[i]))
            {
                s1 += s[i];
            }
        }
        string s2 = "";
        s2 = s1;
        //transform(s1.begin(), s1.end(), s1.begin(), ::tolower);
        //transform(s2.begin(), s2.end(), s2.begin(), ::tolower);
        reverse(s1.begin(), s1.end());
        cout << s2 << " " << s1 << endl;
        if (s2 == s1)
            return true;
        else
            return false;
    }
};