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2024 Day16 Part2 WIP still passing tests
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@smabuk
smabuk committed Dec 16, 2024
1 parent f17f9d4 commit 6053c26
Showing 1 changed file with 39 additions and 31 deletions.
70 changes: 39 additions & 31 deletions Solutions/2024/Day16.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ public static partial class Day16 {
private const char START = 'S';
private const char END = 'E';
private const char WALL = '#';
private const int TURN_COST = 1000;

private static char[,] _maze = default!;
private static Action<string[], bool>? _visualise = null;
Expand All @@ -29,9 +30,9 @@ public static int Part1(string[] _)
ReindeerPosition reindeerPosition = new(_maze.ForEachCell().Single(c => c.Value is START).Index, East);
Point end = _maze.ForEachCell().Single(c => c.Value is END).Index;

(int lowestScore, List<Point> route) = _maze.FindShortestPath(reindeerPosition, end);
(int lowestScore, List<ReindeerPosition> route) = _maze.FindShortestPath(reindeerPosition, end);

_maze.VisualiseMaze($"Lowest Score {lowestScore}:", route);
_maze.VisualiseMaze($"Lowest Score {lowestScore}:", route[1..^1]);

return lowestScore;
}
Expand All @@ -41,59 +42,59 @@ public static int Part2(string[] _)
ReindeerPosition reindeerPosition = new(_maze.ForEachCell().Single(c => c.Value is START).Index, East);
Point end = _maze.ForEachCell().Single(c => c.Value is END).Index;

List<(int Score, List<Point> Route)> routes = [.. _maze.FindAllPaths(reindeerPosition, end)];
List<(int Score, List<ReindeerPosition> Route)> routes = [.. _maze.FindAllPaths(reindeerPosition, end)];
int lowestScore = routes.Min(route => route.Score);

List<Point> tiles = [..routes.Where(r => r.Score == lowestScore).SelectMany(p => p.Route).Distinct()];
_maze.VisualiseMaze($"Tiles:", tiles);
List<ReindeerPosition> tiles = [..routes.Where(r => r.Score == lowestScore).SelectMany(p => p.Route)];
_maze.VisualiseMaze($"Tiles:", tiles.Select(r => r with { Direction = None }));

return tiles.Count;
return tiles.Select(p => p.Position).Distinct().Count();
}

private static IEnumerable<(int, List<Point>)> FindAllPaths(this char[,] maze, ReindeerPosition start, Point end)
private static IEnumerable<(int, List<ReindeerPosition>)> FindAllPaths(this char[,] maze, ReindeerPosition start, Point end)
{
Queue<(int, List<Point>, Direction)> queue = new();
queue.Enqueue((0, new List<Point> { start.Position }, start.Direction));
HashSet<Point> visited = [];
Queue<(int, List<ReindeerPosition>, Direction)> queue = new();
queue.Enqueue((0, new List<ReindeerPosition> { start }, start.Direction));
HashSet<ReindeerPosition> visited = [];

while (queue.Count > 0) {
(int currentDist, List<Point> path, Direction prevDir) = queue.Dequeue();
Point position = path[^1];
(int currentDist, List<ReindeerPosition> path, Direction prevDir) = queue.Dequeue();
ReindeerPosition reindeerPosition = path[^1];


if (position == end) {
if (reindeerPosition.Position == end) {
yield return (currentDist, [.. path]);
continue;
}

_ = visited.Add(position);
_ = visited.Add(reindeerPosition);

foreach (Direction direction in Directions.NESW) {
Point newPosition = position + direction.Delta();
ReindeerPosition newPosition = reindeerPosition with { Position = reindeerPosition.Position + direction.Delta(), Direction = direction};

if (maze.TryGetValue(newPosition, out char value) && value is not WALL
&& !path.Contains(newPosition)
//&& !visited.Contains(newPosition)
if (maze[newPosition.Position.X, newPosition.Position.Y] is not WALL
//&& path.DoesNotContain(newPosition)
&& visited.DoesNotContain(newPosition)
)
{
int turnCost = prevDir != direction ? 1000 : 0;
int turnCost = (prevDir != direction) ? TURN_COST : 0;
int newDist = currentDist + 1 + turnCost;
List<Point> newPath = [.. path, newPosition];
List<ReindeerPosition> newPath = [.. path, newPosition];
queue.Enqueue((newDist, newPath, direction));
}
}
}
}

private static (int, List<Point>) FindShortestPath(this char[,] maze, ReindeerPosition start, Point end)
private static (int, List<ReindeerPosition>) FindShortestPath(this char[,] maze, ReindeerPosition start, Point end)
{
int noOfRows = maze.RowsCount();
int noOfCols = maze.ColsCount();

int[,] distances = new int[noOfCols, noOfRows];
Point[,] previous = new Point[noOfCols, noOfRows];
ReindeerPosition[,] previous = new ReindeerPosition[noOfCols, noOfRows];
distances.FillInPlace(int.MaxValue);
previous.FillInPlace(new Point(-1, -1));
previous.FillInPlace(new ReindeerPosition(new Point(-1, -1), None));

distances[start.Position.X, start.Position.Y] = 0;
PriorityQueue<(int, Point, Direction), int> pq = new();
Expand All @@ -103,8 +104,8 @@ private static (int, List<Point>) FindShortestPath(this char[,] maze, ReindeerPo
(int currentDist, Point position, Direction prevDir) = pq.Dequeue();

if (position ==end) {
List<Point> path = [];
for (Point at = end; at.X != -1 && at.Y != -1; at = previous[at.X, at.Y]) {
List<ReindeerPosition> path = [];
for (ReindeerPosition at = new(end, None); at.Position.X != -1 && at.Position.Y != -1; at = previous[at.Position.X, at.Position.Y]) {
path.Add(at);
}

Expand All @@ -116,11 +117,11 @@ private static (int, List<Point>) FindShortestPath(this char[,] maze, ReindeerPo
Point newPosition = position + direction.Delta();

if (maze.TryGetValue(newPosition, out char value) && value is not WALL) {
int turnCost = (prevDir != direction) ? 1000 : 0;
int turnCost = (prevDir != direction) ? TURN_COST : 0;
int newDist = currentDist + 1 + turnCost;
if (newDist < distances[newPosition.X, newPosition.Y]) {
distances[newPosition.X, newPosition.Y] = newDist;
previous[newPosition.X, newPosition.Y] = position;
previous[newPosition.X, newPosition.Y] = new (position, direction);
pq.Enqueue((newDist, newPosition, direction), newDist);
}
}
Expand All @@ -137,19 +138,26 @@ private record Step(ReindeerPosition Position, Direction PreviousDirection)
public int Score => Position.Direction != PreviousDirection ? 1001 : 1;
}

private static void VisualiseMaze(this char[,] map, string title, IEnumerable<Point>? route = null, bool clearScreen = false)
private static void VisualiseMaze(this char[,] map, string title, IEnumerable<ReindeerPosition>? route = null, bool clearScreen = false)
{
if (_visualise is null) {
return;
}

char[,] outputMap = (char[,])map.Clone();

foreach (Point point in route ?? []) {
outputMap[point.X, point.Y] = 'O';
foreach (ReindeerPosition reindeerPosition in route ?? []) {
outputMap[reindeerPosition.Position.X, reindeerPosition.Position.Y] = reindeerPosition.Direction switch
{
North => '^',
East => '>',
West => '<',
South => 'v',
_ => 'O',
};
}

string[] output = ["", title, .. outputMap.AsStrings()];
string[] output = ["", title, .. outputMap.AsStrings().Select(s => s.Replace('.', ' '))];
_visualise?.Invoke(output, clearScreen);
}
}

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