Задача: Пропущенная двоичная строка

FindMissedBinaryString.cs

using System;
using System.Collections.Generic;
					
public class Program
{
	public static string ConvertNumToBinaryString(int num, int length)
	{
		string binary = Convert.ToString(num, 2);

		// добавляем ведущие нули до размера length
		// Например, length = 5, binary = 101 -> "00101"
		if (binary.Length < length) 
		{
		    binary = string.Concat(System.Linq.Enumerable.Repeat("0", length - binary.Length)) + binary;
		}

		return binary;
	}

	public static string FindMissedBinaryString(string[] nums) {
		var set = new HashSet<string>(nums);
		var len = nums[0].Length;
		int digitNum = (int)Math.Pow(2, len);

		for (int i = 0; i < digitNum; i++)
		{
		    string binary = ConvertNumToBinaryString(i, len);
		    if (!set.Contains(binary)) 
		    {
			return binary;
		    }
		}

		return "";
	}

	public static void Main()
	{
		Console.WriteLine("UniLecs");

		// tests
		Console.WriteLine(FindMissedBinaryString(new string[] { "01", "10" })); // "00"
		Console.WriteLine(FindMissedBinaryString(new string[] { "000", "111","011","001" })); // "010"
	}
}