LeetCode 0125 - Valid Palindrome

class Solution {
public:
    bool isPalindrome(string s) {
        string res = "";
        for(auto it : s) {
            if((it >= 'a' && it <= 'z') || (it >= '0' && it <= '9'))
                res += it;
            else if(it >= 'A' && it <= 'Z')
                res += it + 'a' - 'A';
        }
        for(int i = 0, j = res.size()-1; i <= j; i++, j--) {
            if(res[i] != res[j])
                return 0;
        }
        return 1;
    }
};