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)


private static void Main(string[] args)
public static void WritePermutations()
var permutations = GetPermutations("123");
foreach (var permutation in permutations)
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;
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}";


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