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Combinatorics library (Silverlight for Windows Phone)

I recently found a very nice article at CodeProject on Combinatorics algorithms implementation (specifically Permutations, Combinations and Variations with Repetition option) using C# Generics:


It uses a lexicographic algorithm, so it allows one to ask for “next” permutation/combination/variation from the collection of all possible ones, in the spirit of C++ Standard Library’s (STL) “next_permutation” algorithm.

My Anagram app for Windows Phone 7 is using this code (packed it in a Silverlight library)

I packed the files in a Silverlight for Windows Phone class library (named Combinatorics) and modification I had to do was to:

  1. make the IMetaCollection interface public so that I could abstract the use of any combinatorics operation based on user selection
  2. add CombinatoricsOp class to help with using any combinatorics operation via one entry point
  3. As a bonus there is also a Combinatorics.cd there (class diagram)

You can download the library to use with your WP7 Silverlight apps (or repack source into other library project for other targets) from my Zoomicon public SkyDrive folder:
Please give due credit to original author of Combinatorics code (and myself if you use my additions too).

The code for CombinatoricsOp class I added is below. Just call GetCombinatoricsOp to get a Permutations, Combinations or Variations class instance (all implement IMetaCollection interface) and then use the enumerator (with extra method to get count of items without counting them one-by-one) as described in the CodeProject article mentioned above.

//Version: 20111119
//Author: George Birbilis (birbilis@kagi.com)

using System;
using System.Collections.Generic;   namespace Facet.Combinatorics
{   public static class CombinatoricsOp {   public enum CombinatoricsOpType
      Permutations = 0,
      PermutationsWithRepetition = 1,
      Combinations = 2,
      CombinationsWithRepetition = 3,
      Variations = 4,
      VariationsWithRepetition = 5
    }   public static IMetaCollection<string> GetCombinatoricsOp(
IList<string> values, CombinatoricsOpType opType, int take){ switch (opType) { case CombinatoricsOpType.Permutations: return new Permutations<string>(values);

case CombinatoricsOpType.PermutationsWithRepetition: return new Permutations<string>(values,GenerateOption.WithRepetition); case CombinatoricsOpType.Combinations: return new Combinations<string>(values, take); case CombinatoricsOpType.CombinationsWithRepetition: return new Combinations<string>(
values, take, GenerateOption.WithRepetition); case CombinatoricsOpType.Variations: return new Variations<string>(values, take); case CombinatoricsOpType.VariationsWithRepetition: return new Variations<string>(
values, take, GenerateOption.WithRepetition); default: throw new NotImplementedException(); } }   }   }
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