AdventOfCodeDay17.cs

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

namespace AdventOfCodeDay17
{
	class Program
	{
		static void Main(string[] args)
		{
			var input = new[] { 50, 44, 11, 49, 42, 46, 18, 32, 26, 40, 21, 7, 18, 43, 10, 47, 36, 24, 22, 40 };

			var subsets = input.ToList().Subsets().Where(a => a.Sum() == 150);
			var min = subsets.Min(a => a.Count(b => b != 0));
			var part2 = subsets.Where(a => a.Count(b => b != 0) == min).Count();
			
			Console.WriteLine($"Number of combinations: {subsets.Count()}");
			Console.WriteLine($"Number of combinations: {part2}");
			Console.ReadLine();
		}
	}

	public static class Extensions
	{
		public static IEnumerable<IEnumerable<T>> Subsets<T>(this IList<T> set)
		{
			var state = new BitArray(set.Count);
			do
			{
				yield return Enumerable.Range(0, state.Count).Select(i => state[i] ? set[i] : default(T));
			}
			while (Increment(state));
		}

		public static bool Increment(BitArray flags)
		{
			int x = flags.Count - 1;
			while (x >= 0 && flags[x]) flags[x--] = false;
			if (x >= 0) flags[x] = true;
			return x >= 0;
		}
	}
}