aoc2019/lib/Extensions.cs

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

namespace aoc2019.lib
{
    public static class Extensions
    {
        public static IEnumerable<IEnumerable<T>> Permute<T>(this IEnumerable<T> list)
        {
            if (list.Count() == 1) return new[] { list };
            return list.SelectMany(t => Permute(list.Where(x => !x.Equals(t))), (v, p) => p.Prepend(v));
        }

        public static IEnumerable<string> Chunk(this string str, int chunkSize)
        {
            for (int i = 0; i < str.Length; i += chunkSize)
                yield return str.Substring(i, chunkSize);
        }

        public static string ToDelimitedString<T>(this IEnumerable<T> enumerable, string delimiter = "")
        {
            return string.Join(delimiter, enumerable);
        }

        public static IEnumerable<T> Repeat<T>(this IEnumerable<T> sequence, int? count = null)
        {
            while (count == null || count-- > 0)
                foreach (var item in sequence)
                    yield return item;
        }
    }
}