Algorithms/Shufflers/RecursiveShuffler.cs

using System;

namespace Algorithms.Shufflers
{
    //github.com/ <summary>
    //github.com/     Recursive Shuffler is a recursive version of
    //github.com/     Fisher-Yates shuffle algorithm. This can only be used
    //github.com/     for educational purposes due to stack depth limits.
    //github.com/ </summary>
    //github.com/ <typeparam name="T">Type array input.</typeparam>
    public class RecursiveShuffler<T> : IShuffler<T>
    {
        //github.com/ <summary>
        //github.com/ This is the public overload method that calls the private overload method.
        //github.com/ </summary>
        //github.com/ <param name="array">Array to shuffle.</param>
        //github.com/ <param name="seed">Random generator seed. Used to repeat the shuffle.</param>
        public void Shuffle(T[] array, int? seed = null)
        {
            Shuffle(array, array.Length - 1, seed);
        }

        //github.com/ <summary>
        //github.com/ First, it will check the length of the array on the base case.
        //github.com/ Next, if there's still items left, it will shuffle the sub-array.
        //github.com/ Lastly, it will randomly select index from 0 to number of items of the array
        //github.com/ then swap the elements array[items] and array[index].
        //github.com/ </summary>
        //github.com/ <param name="array">Array to shuffle.</param>
        //github.com/ <param name="items">Number of items in the array.</param>
        //github.com/ <param name="seed">Random generator seed. Used to repeat the shuffle.</param>
        private void Shuffle(T[] array, int items, int? seed)
        {
            if (items <= 0)
            {
                return;
            }

            Shuffle(array, items - 1, seed);
            var random = seed is null ? new Random() : new Random(seed.Value);
            int index = random.Next(items + 1);
            (array[items], array[index]) = (array[index], array[items]);
            (array[items], array[index]) = (array[index], array[items]);
        }
    }
}