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Commit 00e9bc4

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Add recursive shuffling algorithm (#519)
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using Algorithms.Shufflers;
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using Algorithms.Tests.Helpers;
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using FluentAssertions;
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using NUnit.Framework;
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using System;
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namespace Algorithms.Tests.Shufflers
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{
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public static class RecursiveShufflerTests
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{
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[Test]
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public static void ArrayShuffled_NewArraySameSize(
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[Random(10, 1000, 100, Distinct = true)]
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int n)
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{
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// Arrange
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var shuffler = new RecursiveShuffler<int>();
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var (correctArray, testArray) = RandomHelper.GetArrays(n);
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// Act
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shuffler.Shuffle(testArray);
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// Assert
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testArray.Length.Should().Be(correctArray.Length);
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}
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[Test]
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public static void ArrayShuffled_NewArraySameValues(
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[Random(10, 1000, 100, Distinct = true)]
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int n)
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{
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// Arrange
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var shuffler = new RecursiveShuffler<int>();
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var (correctArray, testArray) = RandomHelper.GetArrays(n);
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// Act
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shuffler.Shuffle(testArray);
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// Assert
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testArray.Should().BeEquivalentTo(correctArray);
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}
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[Test]
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public static void ArrayShuffled_NewArraySameShuffle(
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[Random(0, 1000, 2, Distinct = true)] int n,
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[Random(1000, 10000, 5, Distinct = true)] int seed)
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{
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// Arrange
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var shuffler = new RecursiveShuffler<int>();
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var (correctArray, testArray) = RandomHelper.GetArrays(n);
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// Act
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shuffler.Shuffle(testArray, seed);
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shuffler.Shuffle(correctArray, seed);
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// Assert
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correctArray.Should().BeEquivalentTo(testArray, options => options.WithStrictOrdering());
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}
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}
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}
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using System;
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namespace Algorithms.Shufflers
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{
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/// <summary>
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/// Recursive Shuffler is a recursive version of
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/// Fisher-Yates shuffle algorithm. This can only be used
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/// for educational purposes due to stack depth limits.
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/// </summary>
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/// <typeparam name="T">Type array input.</typeparam>
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public class RecursiveShuffler<T> : IShuffler<T>
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{
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/// <summary>
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/// This is the public overload method that calls the private overload method.
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/// </summary>
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/// <param name="array">Array to shuffle.</param>
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/// <param name="seed">Random generator seed. Used to repeat the shuffle.</param>
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public void Shuffle(T[] array, int? seed = null)
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{
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Shuffle(array, array.Length - 1, seed);
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}
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/// <summary>
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/// First, it will check the length of the array on the base case.
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/// Next, if there's still items left, it will shuffle the sub-array.
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/// Lastly, it will randomly select index from 0 to number of items of the array
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/// then swap the elements array[items] and array[index].
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/// </summary>
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/// <param name="array">Array to shuffle.</param>
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/// <param name="items">Number of items in the array.</param>
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/// <param name="seed">Random generator seed. Used to repeat the shuffle.</param>
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private void Shuffle(T[] array, int items, int? seed)
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{
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if (items <= 0)
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{
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return;
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}
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Shuffle(array, items - 1, seed);
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var random = seed is null ? new Random() : new Random(seed.Value);
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int index = random.Next(items + 1);
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(array[items], array[index]) = (array[index], array[items]);
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(array[items], array[index]) = (array[index], array[items]);
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}
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}
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}

‎README.md

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* [Fisher-Yates Shuffler](./Algorithms/Shufflers/FisherYatesShuffler.cs)
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* [LINQ Shuffler](./Algorithms/Shufflers/LinqShuffler.cs)
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* [Naive Shuffler](./Algorithms/Shufflers/NaiveShuffler.cs)
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* [Recursive Shuffler](./Algorithms/Shufflers/RecursiveShuffler.cs)
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* [Sequences](./Algorithms/Sequences)
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* [A000002 Kolakoski](./Algorithms/Sequences/KolakoskiSequence.cs)
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* [A000004 Zero](./Algorithms/Sequences/ZeroSequence.cs)

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