Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Valid Palindrome.cpp

class Solution {
public:
    bool isPalindrome(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        string tmp = "";
        for(int i = 0; i < s.length(); ++i) {
            if(!islower(s[i])) {
                s[i] = tolower(s[i]);
                
            }
            
            if(isalnum(s[i])) {
                tmp += s[i];
            }
        }
        
        
        for(int i = 0; i < tmp.length(); ++i) {
            char cur = tmp[i];
            char opposite = tmp[tmp.length() - i - 1];
            
            if(cur != opposite) {
                return false;
            }
            
        }
        
        return true;
        
        
        
    }
};