Day01.cs

namespace aoc.Year2024;

internal partial class Day01
{
	private readonly Example example = new(
		"""
		3   4
		4   3
		2   5
		1   3
		3   9
		3   3
		""");
	
	public (int[] first, int[] second) Parse(string input)
	{
		var parser =
			Numerics.IntegerInt32.ThenIgnore(SpanX.Space)
				.Then(Numerics.IntegerInt32)
				.Lines()
				.Select(lines => (
					lines.Select(x => x.Item1).ToArray(),
					lines.Select(x => x.Item2).ToArray()
				));

		return parser.Parse(input);
	}

	internal partial class Part1
	{
		public Part1()
		{
			Expect(example, 11);
		}

		public int Solve((int[] first, int[] second) input)
		{
			var totalDifference =
				input.first.Order()
					.Zip(input.second.Order(), Distance).Sum();
			
			return totalDifference;
			
			int Distance(int x, int y) => Math.Abs(x - y);
		}
	}

	internal partial class Part2
	{
		public Part2()
		{
			Expect(example, 31);
		}

		public int Solve((int[] first, int[] second) input)
		{
			var secondGroups = input.second.ToLookup(x => x);
				
			var similarityScore = input.first.Select(x => x * secondGroups[x].Count()).Sum();

			return similarityScore;
		}
	}
}