using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        //Console.WriteLine("Hello World");

        var strTest1 = "{1/[5/(1+2)+2*(3^5-1) +4] *(9+3)}";

        var strTest2 = "{{{}}()}";

        bool res = CheckParens(strTest2);

        Console.WriteLine(res);

    }

    private static bool CheckParens(string str)

    {

        Func<string, int, int> checkRec = null;

        checkRec = (s, idx) => {

            while (true)

            {

                // Eat all up to first open/closed paren.

                while (true)

                {

                    if (idx == s.Length)

                        return idx;

                    if (IsOpenParen(s[idx]))

                        break;

                    if (IsClosedParen(s[idx]))

                        return idx;

                    idx++;

                }

                char openParen = s[idx];

                idx = checkRec(s, idx + 1);

                if (idx < 0 || idx == s.Length || !ParensMatch(openParen, s[idx]))

                    return -1; // error

                if (++idx == s.Length)

                    break;

            }

            return idx;

        };

        if (str == null)

            return true;

        int i = checkRec(str, 0);

        if (i < 0 || i < str.Length)

            return false;

        return true;

    }

    private static bool ParensMatch(char pOpen, char pClosed)

    {

        return parensMatcher[pOpen] == pClosed;

    }

    private static bool IsOpenParen(char c)

    {

        return "([{".IndexOf(c) != -1;

    }

    private static bool IsClosedParen(char c)

    {

        return ")]}".IndexOf(c) != -1;

    }

    private static Dictionary<char, char> parensMatcher = new Dictionary<char, char>(){ {'(', ')'}, { '[', ']' }, { '{', '}' } };

}

​