public static string isBalanced(string s)
    {
        Stack<char> brackets = new Stack<char>();
        
        foreach(char bracket in s){
            if(brackets.TryPeek(out char last) && last == Opposite(bracket)) brackets.Pop();
            else brackets.Push(bracket);
        }
        
        if(brackets.Any()) return "NO";
        
        return "YES";
    }
    
    public static char Opposite (char bracket){
        switch(bracket){
            case '}' : return '{';
            case ')' : return '(';
            case ']' : return '[';            
        }
        return default;
        
    }