using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(IsValidReview(""));

        Console.WriteLine(IsValidReview("()"));

        Console.WriteLine(IsValidReview("()[]{}"));

        Console.WriteLine(!IsValidReview("(]"));

        Console.WriteLine(!IsValidReview("([)]"));

        Console.WriteLine(IsValidReview(""));

    }

​

    public static readonly Dictionary<char, char> brackets = new Dictionary<char, char>{{'(', ')'}, {'[', ']'}, {'{', '}'}};

    public static bool IsValidReview(string input)

    {

        var endings = new Stack<char>();

        foreach (var current in input)

        {

            if (brackets.ContainsKey(current))

            {

                endings.Push(brackets[current]);

            }

            else if (endings.Count == 0 || endings.Pop() != current)

            {

                return false;

            }

        }

        return endings.Count == 0;

    }

}