python solutions through day17

2026-06-07 12:45:10 +02:00 · 2024-12-27 16:10:36 -05:00
parent 5c4d5ebb0f
commit 249ab84e46
9 changed files with 1084 additions and 0 deletions
@@ -0,0 +1,135 @@
+import heapq
+
+
+diffs: list[tuple[int, int]] = [
+    (0, 1),  # start at index 0 facing "east"/right
+    (-1, 0),  # up
+    (0, -1),  # left
+    (1, 0),  # down
+]
+
+
+def day16(input: str, part: int) -> int:
+    grid = [list(line) for line in input.splitlines()]
+    start_row: int = 0
+    start_col: int = 0
+    for r in range(len(grid)):
+        for c in range(len(grid[0])):
+            if grid[r][c] == "S":
+                start_row = r
+                start_col = c
+
+    # i think i'd rather write a struct in go... these tuples are easy to make
+    # but annoying to maintain in my head...
+    # score, row, col, dir_index
+    node: tuple[int, int, int, int, set[tuple[int, int]]] = (
+        int(0),
+        start_row,
+        start_col,
+        int(0),
+        set(),
+    )
+    min_heap = [node]
+    heapq.heapify(min_heap)
+
+    coord_to_min_score: dict[tuple[int, int, int], int] = {}
+
+    best_score: int = 1_000_000  # big enough to not interfere with actual input answer
+    final_path_coords: set[tuple[int, int]] = set()
+
+    while len(min_heap) > 0:
+        popped = heapq.heappop(min_heap)
+
+        # part2 exit once best_score is set down to the actual min value
+        if popped[0] > best_score:
+            continue
+
+        # row, col, dir_index
+        coord = (popped[1], popped[2], popped[3])
+        if coord in coord_to_min_score:
+            prev_score = coord_to_min_score[coord]
+            # if previous score at this coord and direction is better then continue
+            if popped[0] > prev_score:
+                continue
+
+        # update best score to reach this coord
+        coord_to_min_score[coord] = popped[0]
+
+        # end reached
+        if grid[popped[1]][popped[2]] == "E":
+            best_score = popped[0]
+            final_path_coords |= popped[4]
+            final_path_coords.add((popped[1], popped[2]))
+            continue
+
+        # in same direction
+        diff = diffs[popped[3]]
+        next = (
+            popped[0] + 1,
+            popped[1] + diff[0],
+            popped[2] + diff[1],
+            popped[3],
+            popped[4] | {(popped[1], popped[2])},
+        )
+        if grid[next[1]][next[2]] in ".E":
+            heapq.heappush(min_heap, next)
+
+        # 90 deg turns
+        heapq.heappush(
+            min_heap,
+            (popped[0] + 1000, popped[1], popped[2], (popped[3] + 1) % 4, popped[4]),
+        )
+        heapq.heappush(
+            min_heap,
+            (popped[0] + 1000, popped[1], popped[2], (popped[3] - 1) % 4, popped[4]),
+        )
+
+    if part == 1:
+        return best_score
+
+    return len(final_path_coords)
+
+
+example = """###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############"""
+
+example2 = """#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################"""
+
+input = open("input.txt").read().strip()
+
+print(f"day16 example: {day16(example, 1)} want 7036")
+print(f"day16 example2: {day16(example2,1)} want 11048")
+print(f"day16 actual: {day16(input,1)} want 83444")
+
+print(f"part2 example: {day16(example,2)} want 45")
+print(f"part2 example2: {day16(example2,2)} want 64")
+print(f"part2 actual: {day16(input,2)} want 483")