INTERVIEW JOB CODING TASKS – Calculate permutations1 min read

Today we are going to continue with interview coding tasks.

I really do hope this, solved, coding task is going to help you during your interview.

Task: Depending on input value i.e. (123) create all permutations i.e:(123,213,231,132,312,321)

Solution:

private static void Main(string[] args)
{
WritePermutations();
Console.ReadLine();
}

public static void WritePermutations()
{
var permutations = GetPermutations("123");
foreach (var permutation in permutations)
{
Console.WriteLine(permutation);
}
}

public static List<string> GetPermutations(string inputString)
{
return IsPermutated(inputString, out var permutations, out var list) ? list : ListOfPermutations(inputString, permutations);
}

private static bool IsPermutated(string inputString, out List<string> permutations, out List<string> list)
{
permutations = new List<string>();
list = null;
if (inputString == null) return true;
if (inputString.Length != 0) return false;
permutations.Add("");
{
list = permutations;
return true;
}
}

private static List<string> ListOfPermutations(string inputString, List<string> permutations)
{
var firstCharacter = inputString[0];
var remainder = inputString.Substring(1);
var words = GetPermutations(remainder);
foreach (var word in words)
{
for (var i = 0; i <= word.Length; i++)
{
permutations.Add(InsertCharacterAt(word, firstCharacter, i));
}
}
return permutations;
}

public static string InsertCharacterAt(string word, char character, int i)
{
var start = word.Substring(0, i);
var end = word.Substring(i);
return $"{start}{character}{end}";
}

Cheers