using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

public class Program

{

    class Process

    {

        public string M1 = "";

        public string M2 = "";

        public List<string> setOfWords;

        public string errMsg = "Selected words were mismatched. Please try it again ";

        public List<List<string>> strList = new List<List<string>>();

        public void startProcess()

        {

            strList.Clear();

            Stack<string> stack = new Stack<string>();

            stack.Push(M1);

            coreProcess(stack);

        }

​

        public void coreProcess(Stack<string> stack)

        {

            string strWord1 = stack.Peek();

            try

            {

                if (returnCount(strWord1, M2) == 0)

                {

                    strList.Add(new List<string>(stack));

                    return;

                }

​

                int n = setOfWords.Count;

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

                {

                    string strWord2 = setOfWords[i];

                    if (stack.Contains(strWord2))

                        continue;

                    if (returnCount(strWord2, strWord1) == 1)

                    {

                        stack.Push(strWord2);

                        coreProcess(stack);

                        stack.Pop();

                    }

                }

            }

            catch

            {

                Console.WriteLine(errMsg);

                System.Environment.Exit(0);

            }

        }

    }

​

    static int returnCount(string firstWord, string secondWord)

    {

        int wordLength = firstWord.Length;

        int cnt = 0;

        for (int x = 0; x < wordLength; x++)

        {

            if (firstWord[x] != secondWord[x])

                cnt++;

        }

​

        return cnt;

    }

​

    public static void Main(string[] args)

    {

        Process process = new Process();

        process.setOfWords = new List<string>{"band", "bond", "bear", "cars", "fond", "food", "foot", "hand", "head"};

        Console.WriteLine("Set of words:" + " " + "(" + string.Join(",", process.setOfWords) + ")");

        //Console.WriteLine("Please choose your first word:");

        process.M1 = "hand";

        //Console.WriteLine("Please choose your second word:");

        process.M2 = "foot";

        process.startProcess();

        if (process.strList.Count == 0)

        {

            Console.WriteLine(process.errMsg);

            System.Environment.Exit(0);

        }

​

        foreach (List<string> list in process.strList)

        {

            //Console.WriteLine("Here are the new set of words:");

            //Console.WriteLine();

            for (int y = list.Count - 1; y >= 0; y--)

            {

                Console.WriteLine(list[y]);

            }

        }

    //Console.Read();

    }

}