Improved Permutations with the BigInteger Data Type: Listing 1

Overall permutations demo program structure.

using System;
using System.Numerics;
namespace ImprovedPermutations
{
  class PermutationsProgram
  {
    static void Main(string[] args)
    {
      Console.WriteLine("\nBegin improved permutations with BigInteger demo\n");

      int n = 3;
      Permutation p1 = new Permutation(n);

      Console.WriteLine("All permutations for order n = 3 are:\n");
      int ct = 0;
      while (p1 != null)
      {
        Console.WriteLine(ct + ": " + p1.ToString());
        p1 = p1.Successor();
        ++ct;
      }

      // demo application to string array
      // demo Factorial function
      // demo Element method

      Console.WriteLine("\nEnd permutations demo\n");
      Console.ReadLine();
    }
  } // class PermutationsProgram

  public class Permutation
  {
    private int n; // order
    private int[] data;

    public Permutation(int n)
    {
      this.n = n;
      this.data = new int[n];
      for (int i = 0; i < n; ++i)
        this.data[i] = i;
    }

    public static BigInteger Factorial(int k) { . . }
    public Permutation Successor() { . . }
    public string[] ApplyTo(string[] arr) { . . }
    public Permutation Element(BigInteger k) { . . }
    public override string ToString() 
    {
      string s = "( ";
      for (int i = 0; i < data.Length; ++i)
        s += data[i] + " ";  // consider StringBuilder
      s += ")";
      return s;
    }
  } // class Permutation
} // ns

About the Author

Dr. James McCaffrey works for Microsoft Research in Redmond, Wash. He has worked on several Microsoft products including Azure and Bing. James can be reached at jamccaff@microsoft.com.

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