How to write a program to find the permutations of a given string in C#(coding interview question)

I really feel challenged in solving this problem. Basically the term permutations means arranging in an unique order(I don't know anything more). I tried finding permutations on a piece of paper, quite easy to think and note them down. Then I tried to write a program for it to find permutations for as many character as we like. I figured to solve the problem in the following way. Hope it will help you learn something. There is fiddle link below. Run it and know how it works.

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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;
        }
    }
}

To know the how the code works check this link: PermutationsOfString(.net fiddle)

using System; using System.Collections.Generic; using System.Linq; namespace StringPermutations { public class Program { public static void Main(string[] args) { Console.Write("Enter a string to permutate: "); var stringText = Console.ReadLine(); var possibilities = GetPossibilities(stringText); foreach (var pos in possibilities) { //if(pos.Length == stringText.Length) // System.IO.File.AppendAllText(@"C:\Users\Snovasys7\Desktop\test.txt", pos + Environment.NewLine); Console.WriteLine(pos); } Console.ReadKey(); } private static List GetPossibilities(string text) { bool reached = false; List possibleStrings = new List(); List possibleInts = new List(); 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 ints = possibleInts.Distinct(); //foreach (var pos in ints) //{ // System.IO.File.AppendAllText(@"C:\Users\Snovasys7\Desktop\ints.txt", pos + Environment.NewLine); //} //return possibleStrings; 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 GetDigitsList(int number) { List digitsList = new List(); 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; } } } }

Amazons coding interview question on possible ways of reaching to top of a stair case with N steps with N step overs

Actually I came across a video in youtube giving an overview on this coding interview question by amazon. I have gone through the question and started coding in c#. Here I solved the problem in my own way to test my skills in programming.

The question is about to find possible number of ways from starting point, all the way to the end with a set of possible step overs. To get a quick understanding I provided an image.

The code I have pasted below is basically a console app created in visual studio. You can create a new console app in your local and paste this code there and run it. If you can refactor the code just refactor it and paste it in the comment below.

To know the how the code works check this link: StairNWays(.net fiddle)

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using System;
using System.Collections.Generic;
using System.Linq;

namespace stairNways
{
    class Program
    {
        static void Main(string[] args)
        {
            int noOfPossibilities;
            int noOfSteps;
            List<int> combinationsList = new List<int>();
            List<int> noOfWaysList = new List<int>();
            bool reached = false;
            Console.Write("Enter the number of steps: ");
            noOfSteps = Convert.ToInt32(Console.ReadLine());
            Console.Write("Enter the number of possible step overs that you want to make: ");
            noOfPossibilities = Convert.ToInt32(Console.ReadLine());
            if (noOfPossibilities > 0)
            {
                Console.WriteLine("Enter the step over values: ");
                for (int i = 0; i < noOfPossibilities; i++)
                {
                    Console.Write("> ");
                    combinationsList.Add(Convert.ToInt32(Console.ReadLine()));
                }
                Console.WriteLine("You can reach your destination in following possible ways");
                do
                {
                    noOfWaysList = GetArray(noOfWaysList, combinationsList, noOfSteps);
                    reached = checkReached(noOfWaysList, noOfSteps);
                } while (!reached);
                Console.WriteLine(">>>>>>>>>>>>>>>>{0}<<<<<<<<<<<<<<<", noOfWaysList.Count());
            }
            else
            {
                Console.WriteLine("you entered an invalid nuber");
            }
            Console.ReadKey();
        }

        private static bool checkReached(List<int> noOfWaysList, int noOfSteps)
        {
            bool reached = true;
            foreach (var nwl in noOfWaysList)
            {
                if (nwl != noOfSteps)
                    reached = false;
            }
            return reached;
        }

        private static List<int> GetArray(List<int> possibleWaysList, List<int> stepOvers, int noOfSteps)
        {
            if (possibleWaysList == null || possibleWaysList.Count() == 0)
            {
                foreach (var stepOver in stepOvers)
                {
                    possibleWaysList.Add(stepOver);
                }
            }
            else
            {
                List<int> dummyList = new List<int>();
                foreach (var pwl in possibleWaysList)
                {
                    if (pwl == noOfSteps)
                    {
                        dummyList.Add(pwl);
                        continue;
                    }

                    foreach (var so in stepOvers)
                    {
                        if ((pwl + so) <= noOfSteps)
                        {
                            dummyList.Add(pwl + so);
                        }
                    }
                }
                return dummyList;
            }
            return possibleWaysList;
        }
    }
}

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