20 Valid Parentheses

水题，能想到stack就能做

bool isValid(string s) {
  stack<char>scheck;
  for (int i = 0; i < s.size(); ++i) {
    if (s[i] == '(' || s[i] == '[' || s[i] == '{'){
      if (s[i] == '(')scheck.push(')');
      else if (s[i] == '{')scheck.push('}');
      else scheck.push(']');
    }
    else {
      
      if (scheck.empty())return false;
      if (s[i] == scheck.top()) {
        scheck.pop();
      }
      else return false;
    }
  }
  if (!scheck.empty())return false;
  return true;
}