day16 - corrected

day16.py

@@ -30,16 +30,35 @@ def get_best_score(grid: Grid) -> tuple[int, set[Coordinate]]:
 def get_tiles_from_all_paths(grid: Grid) -> int:
     target_score, target_path = get_best_score(grid)
     target = Coordinate(grid.maxX - 1, 1)
+
+    path_scores = {}
+    score = 0
+    facing = Coordinate(1, 0)
+    pos = Coordinate(1, grid.maxY - 1)
+    visited = set()
+    while pos != target:
+        visited.add(pos)
+        for n in pos.getNeighbours(includeDiagonal=False):
+            if n not in target_path or n in visited:
+                continue
+
+            if n - pos != facing:
+                score += 1000
+                facing = n - pos
+
+            path_scores[pos] = score
+            pos = n
+            score += 1
+
     queue = [(0, Coordinate(1, grid.maxY - 1), Coordinate(1, 0), {Coordinate(1, grid.maxY - 1)})]
-    # all_paths = set()
     visited = {}
     while queue:
         score, pos, facing, path = heappop(queue)
         if pos in visited and score > visited[pos][0] + 1000:
             continue
-        if pos in target_path and pos in visited:
-            # print(f"{pos} in target_path and visited. {score=}, {visited[pos]=}, discarding {path=}")
-            if score <= visited[pos][0] or score == visited[pos][0] + 1000:
+
+        if pos in path_scores and pos in visited:
+            if score <= path_scores[pos]:
                 target_path |= path
             continue
 
@@ -58,9 +77,6 @@ def get_tiles_from_all_paths(grid: Grid) -> int:
             add_turn = 1001 if n - pos != facing else 1
             heappush(queue, (score + add_turn, n, n - pos, path | {n}))
 
-    for p in target_path:
-        grid.set(p, "O")
-    grid.print()
     return len(target_path)