2024 day 16 no networkx.

src/holt59/aoc/2024/day16.py

@@ -1,7 +1,7 @@
+import heapq
+from collections import defaultdict
 from typing import Any, Iterator, TypeAlias
 
-import networkx as nx
-
 from ..base import BaseSolver
 
 Position: TypeAlias = tuple[int, int]
@@ -18,41 +18,45 @@ class Solver(BaseSolver):
         target = next(
             (i, j) for i in range(n_rows) for j in range(n_cols) if grid[i][j] == "E"
         )
-        facing = (0, 1)
 
-        G = nx.DiGraph()
+        queue: list[tuple[int, Position, Direction, tuple[Position, ...]]] = [
+            (0, rein, (0, 1), (rein,))
+        ]
 
-        for i in range(1, n_rows - 1):
+        max_score = n_rows * n_cols * 1000
-            for j in range(1, n_cols - 1):
+        target_score: int = max_score
-                if grid[i][j] == "#":
+        scores: dict[tuple[Position, Direction], int] = defaultdict(lambda: max_score)
-                    continue
+        visited: set[Position] = set()
 
-                for di, dj in ((-1, 0), (0, 1), (1, 0), (0, -1)):
+        while queue:
-                    if grid[i + di][j + dj] != "#":
+            score, pos, dir, path = heapq.heappop(queue)
-                        G.add_edge(
-                            ((i, j), (di, dj)), ((i + di, j + dj), (di, dj)), weight=1
-                        )
 
-                    if di == 0:
+            if target_score < score:
-                        G.add_edge(((i, j), (di, dj)), ((i, j), (1, 0)), weight=1000)
+                break
-                        G.add_edge(((i, j), (di, dj)), ((i, j), (-1, 0)), weight=1000)
-                    else:
-                        G.add_edge(((i, j), (di, dj)), ((i, j), (0, 1)), weight=1000)
-                        G.add_edge(((i, j), (di, dj)), ((i, j), (0, -1)), weight=1000)
 
-        for di, dj in ((-1, 0), (0, 1), (1, 0), (0, -1)):
+            if pos == target:
-            G.add_edge((target, (di, dj)), (target, (-1, -1)), weight=0)
+                target_score = score
+                visited |= set(path)
+                continue
 
-        yield nx.shortest_path_length(
+            scores[pos, dir] = score
-            G,
-            source=(rein, facing),
-            target=(target, (-1, -1)),
-            weight="weight",
-        )
 
-        nodes: set[tuple[int, int]] = set()
+            row, col = pos
-        for path in nx.all_shortest_paths(
+            d_row, d_col = dir
-            G, source=(rein, facing), target=(target, (-1, -1)), weight="weight"
+
-        ):
+            for cost, n_pos, n_dir in (
-            nodes.update(position for position, _ in path)
+                (1, (row + d_row, col + d_col), dir),
-        yield len(nodes)
+                (1000, pos, (1, 0) if d_row == 0 else (0, 1)),
+                (1000, pos, (-1, 0) if d_row == 0 else (0, -1)),
+            ):
+                n_row, n_col = n_pos
+                score_n = score + cost
+                if grid[n_row][n_col] != "#" and score_n < scores[n_pos, n_dir]:
+                    heapq.heappush(
+                        queue,
+                        (score_n, n_pos, n_dir, path + (n_pos,)),
+                    )
+
+        assert target_score is not None
+        yield target_score
+        yield len(visited)