using System;

using System.Collections.Generic;

​

public class BingoBongo

{

    public static void generateCombinations(String input)

    {

        var combinationList = new List<string>{""};

​

        foreach (char ch in input.ToCharArray())

        {

            int count = combinationList.Count;

​

            for (int i = 0; i < count; i++)

            {

                combinationList.Add(combinationList[i] + ch);

            }

        }

​

        foreach (var result in combinationList)

            Console.WriteLine(result);

    }

​

    public static void Main(string[] args)

    {

        generateCombinations("abcd");

    }

}