The elves bought too much eggnog again - 150 liters this time. To fit it all into your refrigerator, you'll need to move it into smaller containers. You take an inventory of the capacities of the available containers.

For example, suppose you have containers of size 20, 15, 10, 5, and 5 liters. If you need to store 25 liters, there are four ways to do it:

Read the full puzzle.

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

namespace AdventOfCode.Y2015.Day17;

[ProblemName("No Such Thing as Too Much")]
class Solution : Solver {

    public object PartOne(string input) => Fill(Parse(input)).Count();
    public object PartTwo(string input) {
        var combinations = Fill(Parse(input)).ToArray();
        var shortest = combinations.Select(combination => combination.Count()).Min();
        return combinations.Count(combination => combination.Count() == shortest);
    }

    int[] Parse(string input) => input.Split('\n').Select(int.Parse).ToArray();

    IEnumerable<ImmutableList<int>> Fill(int[] containers) {
        IEnumerable<ImmutableList<int>> FillRecursive(int i, int amount) {
            if (i == containers.Length) {
                yield break;
            } else {
                if (amount == containers[i]) {
                    yield return ImmutableList.Create<int>(i);
                }
                if (amount >= containers[i]) {
                    foreach (var v in FillRecursive(i + 1, amount - containers[i])) {
                        yield return v.Add(i);
                    }
                }
                foreach (var v in FillRecursive(i + 1, amount)) {
                    yield return v;
                }
            }
        }

        return FillRecursive(0, 150);
    }
}

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