2023 day 17, v2.

2023/day17.py

@@ -18,7 +18,6 @@ class Label:
     col: int
 
     direction: Direction
-    count: int
 
     parent: Label | None = None
 
@@ -81,7 +80,7 @@ def shortest_many_paths(grid: list[list[int]]) -> dict[tuple[int, int], int]:
     visited: dict[tuple[int, int], tuple[Label, int]] = {}
 
     queue: list[tuple[int, Label]] = [
-        (0, Label(row=n_rows - 1, col=n_cols - 1, direction="^", count=0))
+        (0, Label(row=n_rows - 1, col=n_cols - 1, direction="^"))
     ]
 
     while queue and len(visited) != n_rows * n_cols:
@@ -117,7 +116,6 @@ def shortest_many_paths(grid: list[list[int]]) -> dict[tuple[int, int], int]:
                         row=row,
                         col=col,
                         direction=direction,
-                        count=0,
                         parent=label,
                     ),
                 ),
@@ -137,7 +135,7 @@ def shortest_path(
     target = (len(grid) - 1, len(grid[0]) - 1)
 
     # for each tuple (row, col, direction, count), the associated label when visited
-    visited: dict[tuple[int, int, str, int], Label] = {}
+    visited: dict[tuple[int, int, Direction], Label] = {}
 
     # list of all visited labels for a cell (with associated distance)
     per_cell: dict[tuple[int, int], list[tuple[Label, int]]] = defaultdict(list)
@@ -145,17 +143,17 @@ def shortest_path(
     # need to add two start labels, otherwise one of the two possible direction will
     # not be possible
     queue: list[tuple[int, int, Label]] = [
-        (lower_bounds[0, 0], 0, Label(row=0, col=0, direction="^", count=0)),
-        (lower_bounds[0, 0], 0, Label(row=0, col=0, direction="<", count=0)),
+        (lower_bounds[0, 0], 0, Label(row=0, col=0, direction="^")),
+        (lower_bounds[0, 0], 0, Label(row=0, col=0, direction="<")),
     ]
 
     while queue:
         _, distance, label = heapq.heappop(queue)
 
-        if (label.row, label.col, label.direction, label.count) in visited:
+        if (label.row, label.col, label.direction) in visited:
             continue
 
-        visited[label.row, label.col, label.direction, label.count] = label
+        visited[label.row, label.col, label.direction] = label
         per_cell[label.row, label.col].append((label, distance))
 
         if (label.row, label.col) == target:
@@ -163,57 +161,40 @@ def shortest_path(
 
         for direction, (c_row, c_col, i_direction) in MAPPINGS.items():
             # cannot move in the opposite direction
-            if label.direction == i_direction:
+            if label.direction == i_direction or label.direction == direction:
                 continue
 
-            # other direction, move 'min_straight' in the new direction
-            elif label.direction != direction:
-                row, col, count = (
-                    label.row + min_straight * c_row,
-                    label.col + min_straight * c_col,
-                    min_straight,
+            distance_to = distance
+
+            for amount in range(1, max_straight + 1):
+                row, col = (
+                    label.row + amount * c_row,
+                    label.col + amount * c_col,
                 )
 
-            # same direction, too many count
-            elif label.count == max_straight:
-                continue
+                # exclude labels outside the grid or with too many moves in the same
+                # direction
+                if not (0 <= row < n_rows and 0 <= col < n_cols):
+                    break
 
-            # same direction, keep going and increment count
-            else:
-                row, col, count = (
-                    label.row + c_row,
-                    label.col + c_col,
-                    label.count + 1,
-                )
-            # exclude labels outside the grid or with too many moves in the same
-            # direction
-            if row not in range(0, n_rows) or col not in range(0, n_cols):
-                continue
+                distance_to += grid[row][col]
 
-            distance_to = (
-                distance
-                + sum(
-                    grid[r][c]
-                    for r in range(min(row, label.row), max(row, label.row) + 1)
-                    for c in range(min(col, label.col), max(col, label.col) + 1)
-                )
-                - grid[label.row][label.col]
-            )
+                if amount < min_straight:
+                    continue
 
-            heapq.heappush(
-                queue,
-                (
-                    distance_to + lower_bounds[row, col],
-                    distance_to,
-                    Label(
-                        row=row,
-                        col=col,
-                        direction=direction,
-                        count=count,
-                        parent=label,
+                heapq.heappush(
+                    queue,
+                    (
+                        distance_to + lower_bounds[row, col],
+                        distance_to,
+                        Label(
+                            row=row,
+                            col=col,
+                            direction=direction,
+                            parent=label,
+                        ),
                     ),
-                ),
-            )
+                )
 
     if VERBOSE:
         print_shortest_path(grid, target, per_cell)