Merge pull request #80 from vil02/16_solution

feat: add `adv_2024_16`

solutions/adv_2024_16.py

@@ -0,0 +1,120 @@
+import typing
+import heapq
+import math
+import functools
+
+Pair = tuple[int, int]
+
+_N = (0, -1)
+_S = (0, 1)
+_W = (-1, 0)
+_E = (1, 0)
+
+_DIR_TO_NAME = {
+    _N: "N",
+    _S: "S",
+    _W: "W",
+    _E: "E",
+}
+
+_DIRS = list(_DIR_TO_NAME.keys())
+
+_NEG_DIR = {_N: _S, _S: _N, _W: _E, _E: _W}
+
+
+def _parse_input(in_str: str, wall: str = "#") -> tuple[frozenset[Pair], Pair, Pair]:
+    walls: set[Pair] = set()
+    start = None
+    end = None
+    for y_pos, line in enumerate(in_str.splitlines()):
+        for x_pos, _ in enumerate(line):
+            if _ == wall:
+                walls.add((x_pos, y_pos))
+            elif _ == "S":
+                assert start is None
+                start = (x_pos, y_pos)
+            elif _ == "E":
+                assert end is None
+                end = (x_pos, y_pos)
+    assert start is not None
+    assert end is not None
+    return frozenset(walls), start, end
+
+
+def _shift(in_pos: Pair, shift: Pair) -> Pair:
+    _x, _y = in_pos
+    _sx, _sy = shift
+    res = _x + _sx, _y + _sy
+    return res
+
+
+def _gen_positions(
+    walls: set[Pair], in_pos: Pair, last_dir: Pair
+) -> typing.Generator[tuple[Pair, Pair], None, None]:
+    for new_dir in _DIRS:
+        if new_dir != _NEG_DIR[last_dir]:
+            new_pos = _shift(in_pos, new_dir)
+            if new_pos not in walls:
+                yield new_pos, new_dir
+
+
+def _compute_new_score(cur_score: int, cur_dir: Pair, new_dir: Pair) -> int:
+    assert new_dir != _NEG_DIR[cur_dir]
+    if cur_dir == new_dir:
+        return cur_score + 1
+    return cur_score + 1001
+
+
+@functools.cache
+def _find_best_path(
+    walls: set[Pair], start: Pair, end: Pair
+) -> tuple[int, list[list[Pair]]]:
+    best_score = math.inf
+    best_paths: list[list[Pair]] = []
+    active: list[tuple[int, Pair, Pair, list[Pair]]] = []
+    visited: dict[tuple[Pair, Pair], int] = {}
+    heapq.heappush(active, (0, start, _E, [start]))
+    while active:
+        cur_score, cur_pos, cur_dir, cur_path = heapq.heappop(active)
+        if cur_score > best_score:
+            continue
+        if (cur_pos, cur_dir) in visited and visited[(cur_pos, cur_dir)] < cur_score:
+            continue
+        visited[(cur_pos, cur_dir)] = cur_score
+        if cur_pos == end:
+            if best_score > cur_score:
+                best_score = cur_score
+                best_paths = []
+            best_paths.append(cur_path)
+            continue
+        for new_pos, new_dir in _gen_positions(walls, cur_pos, cur_dir):
+            heapq.heappush(
+                active,
+                (
+                    _compute_new_score(cur_score, cur_dir, new_dir),
+                    new_pos,
+                    new_dir,
+                    cur_path + [new_pos],
+                ),
+            )
+    assert isinstance(best_score, int)
+    return best_score, best_paths
+
+
+def solve_a(in_str: str) -> int:
+    data, start, end = _parse_input(in_str)
+    best_score, _ = _find_best_path(data, start, end)
+    return best_score
+
+
+def _get_all_best_tiles(paths: list[list[Pair]]) -> set[Pair]:
+    res = set()
+    for path in paths:
+        res.update(path)
+    return res
+
+
+def solve_b(in_str: str) -> int:
+    data, start, end = _parse_input(in_str)
+    _, paths = _find_best_path(data, start, end)
+    return len(_get_all_best_tiles(paths))

tests/test_adv_2024_16.py

@@ -0,0 +1,10 @@
+import solutions.adv_2024_16 as sol
+from . import test_utils as tu
+
+
+_INPUTS = tu.get_inputs(16, {"small", "small_2", "p"})
+
+test_solve_a, test_solve_b = _INPUTS.get_tests(
+    (sol.solve_a, sol.solve_b),
+    {"small": (7036, 45), "small_2": (11048, 64), "p": (85432, 465)},
+)