using System;

using System.Collections.Generic;

​

public class Program

{

    static Dictionary<string, string> Match = new Dictionary<string, string>()

    {{"<", ">"}, {"{", "}"}, {"(", ")"}, {"[", "]"}, };

    public static void Main()

    {

        var proper = "{ab(de[ef<gh}}ijk}lmn}";//"{([[]]<>)}";

        var error = "{ab(de[ef<gh>)]ijk)lmn}";

        //Console.WriteLine(error + " is matching: " + FindMatching(error));

        Console.WriteLine(proper + " is matching: " + FindMatching(proper, 0, 0));

    }

​

    static bool FindMatching(string str)

    {

        Stack<string> stack = new();

        for (var i = 0; i < str.Length; i++)

        {

            var text = str[i].ToString();

            if (Match.ContainsKey(text)) //is opening

            {

                stack.Push(Match[text]); //add expected closing to stack

                continue;

            }

​

            if (Match.ContainsValue(text))

            {

                string closing = stack.Pop();

                if (closing != text)

                {

                    return false;

                }

            }

        }

​

        if (stack.Count > 0)

        {

            return false;

        }

​

        return true;

    }

​

    static bool FindMatching(string str, int open, int close)

    {

        if (String.IsNullOrEmpty(str))

        {   

            return open == close;

        }

​

        string text = str[0].ToString();

​

        if (Match.ContainsKey(text))

        {

            return FindMatching(str.Substring(1), open + 1, close);

        }

        else if (Match.ContainsValue(text))

        {

            return FindMatching(str.Substring(1), open, close + 1);

        }

​

        return FindMatching(str.Substring(1), open, close);

    }

}