text:  class Solution {
  public:
      bool XXX(string s) {
  
          string str;
          for(int i = 0; i < s.size(); i++){
              if((tolower(s[i]) >= 'a' && tolower(s[i]) <= 'z') || (s[i] >= '0' && s[i] <= '9')){
                  str += tolower(s[i]);
              }
          }
          int left = 0, right = str.size() - 1;
          while(left <= right){
              if(str[left] != str[right]){
                  return false;
              }
              left++,right--;
          }
          return true;
      }
  };
  
  