permutation

Here's the VB version as promised. Sorry about the quality of the code but as I mentioned in my last post I'm a C# developer. Feel free to refactor! I've included a Main() so that you can see the output.

Imports System.Collections.Generic

Module Module1

Sub Main()

   Dim values() As Integer = {1, 3, 5}

   Dim permList As New List(Of Integer())

   permList = Permute(values)

   Dim perm As Integer()

   For Each perm In permList

      Dim output As String = String.Empty

      Dim value As Integer

      For Each value In perm

         output += value.ToString

         Console.WriteLine(output)

      Next

   Next

   Console.ReadLine()

End Sub

Function Permute(ByVal values() As Integer) As List(Of Integer())

   Dim permList As New List(Of Integer())

   PermuteWorker(values, 0, values.Length, permList)

   Return permList

End Function

Sub PermuteWorker(ByVal values() As Integer, ByVal start As Integer, ByVal n As Integer, ByRef permList As List(Of Integer()))

   If start = n - 1 Then

      Dim thisValues(values.Length) As Integer

      values.CopyTo(thisValues, 0)

      permList.Add(thisValues)

   Else

      Dim i As Integer

      For i = start To n - 1

         Dim tmp As Integer = values(i)

         values(i) = values(start)

         values(start) = tmp

         PermuteWorker(values, start + 1, n, permList)

         values(start) = values(i)

         values(i) = tmp

      Next

   End If

End Sub

End Module

 

Regards

Ashley

Here's an algorithm in C#, based on one published by the University of Exeter school of physics. You need to call the Permute function with an array of integers and a list of integer arrays will be returned. permuteWorker recursively does the actual work.
I know you wanted it in VB but I'm a C# guy primarily and nobody else has responded. I'll post a VB version this evening (UK time), just thought if you wanted it quick that you might be able to convert it.

  public List Permute(int[] values)
        {
            List permList = new List();

            permuteWorker(values, 0, values.Length, ref permList);

            return permList;
        }

        private void permuteWorker(int[] values, int start, int n, ref List permList)
        {
            if (start == n - 1)
            {
                int[] thisValues = new int[values.Length] ;
                values.CopyTo(thisValues, 0);
                permList.Add(thisValues);
            }
            else
            {
                for (int i = start; i < n; i++)
                {
                    int tmp = values[i];

                    values[i] = values[start];
                    values[start] = tmp;
                    permuteWorker(values, start + 1, n, ref permList);
                    values[start] = values[i];
                    values[i] = tmp;
                }
            }
        }

Regards

Ashley