Y23 D25

Author: viceroypenguin

AdventOfCode.Puzzles/2023/day25.original.cs

@@ -0,0 +1,105 @@
+using System.Runtime.InteropServices;
+
+namespace AdventOfCode.Puzzles._2023;
+
+[Puzzle(2023, 25, CodeType.Original)]
+public partial class Day_25_Original : IPuzzle
+{
+	public (string, string) Solve(PuzzleInput input)
+	{
+		var connections = new Dictionary<string, List<string>>();
+		foreach (var line in input.Lines)
+		{
+			var l = line.Split();
+			var from = l[0][..^1];
+
+			foreach (var to in l.Skip(1))
+			{
+				connections.GetOrAdd(from, _ => new())
+					.Add(to);
+				connections.GetOrAdd(to, to => new())
+					.Add(from);
+			}
+		}
+
+		var part1 = 0;
+		var keys = connections.Keys.ToList();
+		foreach (var key in keys.Skip(1))
+		{
+			var setSize = GetComponentSize(connections, keys[0], key);
+			if (setSize > 0)
+			{
+				part1 = setSize * (keys.Count - setSize);
+				break;
+			}
+		}
+
+		return (part1.ToString(), string.Empty);
+	}
+
+	private static int GetComponentSize(
+		Dictionary<string, List<string>> connections, string start, string end)
+	{
+		var flows = new Dictionary<(string from, string to), int>();
+		var numFlows = 0;
+		while (true)
+		{
+			var componentSize = GetComponentSize(connections, flows, start, end);
+			if (componentSize == 0)
+				numFlows++;
+			else if (numFlows == 3)
+				return componentSize;
+			else
+				break;
+		}
+		return 0;
+	}
+
+	private static int GetComponentSize(
+		Dictionary<string, List<string>> connections,
+		Dictionary<(string from, string to), int> flows,
+		string start, string end)
+	{
+		var from = new Dictionary<string, string>()
+		{
+			[start] = start,
+		};
+
+		var steps = 0;
+
+		var queue = new Queue<string>();
+		queue.Enqueue(start);
+
+		while (queue.TryDequeue(out var current) && !from.ContainsKey(end))
+		{
+			steps++;
+
+			var list = connections[current];
+			foreach (var dest in connections.Keys)
+			{
+				var rate = (list.Contains(dest) ? 1 : 0) - flows.GetValueOrDefault((current, dest));
+				if (rate > 0 && !from.ContainsKey(dest))
+				{
+					from[dest] = current;
+					queue.Enqueue(dest);
+				}
+			}
+		}
+
+		if (!from.ContainsKey(end))
+			return steps;
+
+		var cur = end;
+		while (cur != start)
+		{
+			CollectionsMarshal.GetValueRefOrAddDefault(
+				flows, (from[cur], cur), out _) += 1;
+			CollectionsMarshal.GetValueRefOrAddDefault(
+				flows, (cur, from[cur]), out _) -= 1;
+
+			cur = from[cur];
+		}
+
+		return 0;
+	}
+}