feat: solved day 16 part 2

2024-12-17 22:58:51 -06:00
parent 5b7dbd5b1d
commit 655b1ffd8f
8 changed files with 209 additions and 88 deletions
@@ -0,0 +1,111 @@
+namespace ReindeerMaze;
+
+static class PuzzleSolver
+{
+  public static int Solve(string[] input, bool isPart2 = false)
+  {
+    List<Direction> directions = [
+      Direction.Right, 
+      Direction.Down, 
+      Direction.Left,
+      Direction.Up,
+    ];
+    
+    var rows = input.Length;
+    var columns = input[0].Length;
+
+    var startPosition = new Position(-1, -1);
+    var endPosition = new Position(-1, -1);
+    
+    for (var row = 0; row < rows; row++)
+    {
+      for (var column = 0; column < columns; column++)
+      {
+        var currentValue = input[row][column];
+
+        switch (currentValue)
+        {
+          case 'S':
+            startPosition = new(column, row);
+            break;
+          case 'E':
+            endPosition = new(column, row);
+            break;
+        }
+      }
+    }
+
+    var queue = new PriorityQueue<MazePath, int>();
+    var visitedTiles = new HashSet<Tile>();
+    var initialScore = 0;
+    var initialDirection = 0;
+    var startTile = new Tile(startPosition, initialDirection);
+    var bestScore = int.MaxValue;
+    var bestPath = new MazePath([startTile], initialScore);
+    HashSet<Position> bestSeats = [startPosition];
+    
+    queue.Enqueue(bestPath, initialScore);
+    
+    while (queue.Count is not 0)
+    {
+      var path = queue.Dequeue();
+      var currentTile = path.CurrentTile;
+      var currentScore = path.Score;
+      
+      if (currentScore > bestScore)
+      {
+        break;
+      }
+
+      if (currentTile.Position == endPosition)
+      {
+        bestScore = currentScore;
+        bestSeats.UnionWith(path.Tiles.Select(t => t.Position));
+        continue;
+      }
+      
+      visitedTiles.Add(currentTile);
+      
+      var currentDirection = directions[currentTile.DirectionIndex];
+      var nextPosition = currentTile.Position.GetNextPosition(currentDirection);
+
+      if (
+        nextPosition.X >= 0 && 
+        nextPosition.X < columns && 
+        nextPosition.Y >= 0 && 
+        nextPosition.Y < rows && 
+        input[nextPosition.Y][nextPosition.X] != '#'
+      )
+      {
+        var newScoreAfterMovingForward = currentScore + 1;
+        var nextTileAfterMovingForward = currentTile with { Position = nextPosition };
+        var nextPath = new MazePath([..path.Tiles, nextTileAfterMovingForward], newScoreAfterMovingForward);
+
+        if (visitedTiles.Contains(nextTileAfterMovingForward) is false)
+        {
+          queue.Enqueue(nextPath, newScoreAfterMovingForward);
+        }
+      }
+ 
+      var newScoreAfterTurning = currentScore + 1000;
+      
+      var directionAfterClockWiseTurn = (currentTile.DirectionIndex + 1) % directions.Count;
+      var nextTileAfterClockWiseTurn = currentTile with { DirectionIndex = directionAfterClockWiseTurn };
+
+      if (visitedTiles.Contains(nextTileAfterClockWiseTurn) is false)
+      {
+        queue.Enqueue(new([..path.Tiles, nextTileAfterClockWiseTurn], newScoreAfterTurning), newScoreAfterTurning);
+      }
+      
+      var directionAfterCounterClockWiseTurn = (currentTile.DirectionIndex + 3) % directions.Count;
+      var nextTileAfterCounterClockWiseTurn = currentTile with { DirectionIndex = directionAfterCounterClockWiseTurn };
+
+      if (visitedTiles.Contains(nextTileAfterCounterClockWiseTurn) is false)
+      {
+        queue.Enqueue(new([..path.Tiles, nextTileAfterCounterClockWiseTurn], newScoreAfterTurning), newScoreAfterTurning);
+      }
+    }
+    
+    return isPart2 ? bestSeats.Count : bestScore;
+  }
+}