using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main(string[] args)

    {            

        var stringText = "ABCD";

        var possibilities = GetPossibilities(stringText);

        Console.WriteLine("The permutations of *{0}* are as shown below:", stringText);

        foreach (var pos in possibilities)

        {

            Console.WriteLine(">>>>>>>>>>>>>>" + pos + "<<<<<<<<<<<<<<");

        }

    }

​

    private static List<string> GetPossibilities(string text)

    {

        bool reached = false;

        List<string> possibleStrings = new List<string>();

        List<int> possibleInts = new List<int>();

        var textArray = text.ToArray();

        string prev = string.Empty;

        string dummy = string.Empty;

        int preIndexNum = 1;

        while (!reached)

        {

            var indexes = GetDigitsList(preIndexNum);

            foreach (var index in indexes)

            {

                dummy = dummy + textArray[index - 1];

            }

            bool isPermutation = CheckPermutation(dummy, text);

            if (isPermutation)

            {

                possibleStrings.Add(dummy);

                possibleInts.Add(preIndexNum);

            }

            dummy = string.Empty;

            reached = checkReached(preIndexNum, textArray.Length);

            preIndexNum = GetNumberBasedOnTextLength(textArray.Length, preIndexNum);

        }

        var distinctStrings = possibleStrings.Distinct().ToList();

        return distinctStrings;

    }

    private static bool CheckPermutation(string dummy, string text)

    {

        if (dummy.Count() != text.Length)

            return false;

        else

        {

            foreach (var t in dummy)

            {

                if (dummy.Count(x => x == t) == text.Count(x => x == t))

                    continue;

                else

                    return false;

            }

            return true;

        }

    }

    private static int GetNumberBasedOnTextLength(int length, int number)

    {

        var digitsList = GetDigitsList(number);

        digitsList.Reverse();

        var digitsArray = digitsList.ToArray();

        var dummyIntList = new int[digitsArray.Length + 1];

        for (int i = 0; i < digitsArray.Length; i++)

        {

            dummyIntList[i] = digitsArray[i];

        }

        for (int i = 0; i < dummyIntList.Length; i++)

        {

            if (dummyIntList[i] < length)

            {

                dummyIntList[i] = dummyIntList[i] + 1;

                break;

            }

            if (dummyIntList[i] == length)

            {

                for (int j = i; j < dummyIntList.Length; j++)

                {

                    if (dummyIntList[j] < length)

                    {

                        dummyIntList[j] = dummyIntList[j] + 1;

                        break;

                    }

                    else

                        dummyIntList[j] = 1;

                }

                break;

            }

        }

        var list = dummyIntList.ToList();

        list.Reverse();

        number = GenrateNumber(list.ToArray());

        return number;

    }

    private static int GenrateNumber(int[] digitsArray)

    {

        int sum = 0;

        for (int i = 0; i < digitsArray.Length; i++)

        {

            if (digitsArray[i] == 0)

                continue;

            sum = sum * 10 + digitsArray[i];

        }

        return sum;

    }

    private static List<int> GetDigitsList(int number)

    {

        List<int> digitsList = new List<int>();

        while (number > 0)

        {

            digitsList.Add(number % 10);

            number = number / 10;

        }

        digitsList.Reverse();

        return digitsList;

    }

    private static bool checkReached(int preIndexNum, int length)

    {

        var digitsList = GetDigitsList(preIndexNum);

        if (digitsList.Count() == length)

        {

            foreach (var digit in digitsList)

            {

                if (digit < length)

                    return false;

            }

            return true;

        }

        else

        {

            return false;

        }

    }

}