using System.Collections.Generic;
using System.Linq;
using System.Numerics;

namespace Algorithms.Sequences
{
    /// <summary>
    ///     <para>
    ///         Golomb's sequence. a(n) is the number of times n occurs in the sequence, starting with a(1) = 1.
    ///     </para>
    ///     <para>
    ///         Wikipedia: https://en.wikipedia.org/wiki/Golomb_sequence.
    ///     </para>
    ///     <para>
    ///         OEIS: https://oeis.org/A001462.
    ///     </para>
    /// </summary>
    public class GolombsSequence : ISequence
    {
        /// <summary>
        ///     Gets Golomb's sequence.
        /// </summary>
        public IEnumerable<BigInteger> Sequence
        {
            get
            {
                yield return 1;
                yield return 2;
                yield return 2;

                var queue = new Queue<BigInteger>();
                queue.Enqueue(2);

                for (var i = 3; ; i++)
                {
                    var repetitions = queue.Dequeue();
                    for (var j = 0; j < repetitions; j++)
                    {
                        queue.Enqueue(i);
                        yield return i;
                    }
                }
            }
        }
    }
}
