Day 16

aoc_cas/aoc2023/day16.py

@@ -0,0 +1,109 @@
+import dataclasses
+from enum import Enum
+from functools import cache
+from typing import Self, Sequence
+
+
+class Direction(Enum):
+    UP = (-1, 0)
+    LEFT = (0, -1)
+    DOWN = (1, 0)
+    RIGHT = (0, 1)
+
+
+@dataclasses.dataclass(frozen=True)
+class Coordinate:
+    y: int
+    x: int
+
+    @cache
+    @staticmethod
+    def create(y: int, x: int) -> "Coordinate":
+        return Coordinate(y, x)
+
+    def move(self, dir: Direction, k: int = 1) -> Self:
+        return Coordinate.create(self.y + dir.value[0] * k, self.x + dir.value[1] * k)
+
+
+reflections: dict[str, dict[Direction, tuple[Direction, ...]]] = {
+    "/": {
+        Direction.UP: (Direction.RIGHT,),
+        Direction.LEFT: (Direction.DOWN,),
+        Direction.DOWN: (Direction.LEFT,),
+        Direction.RIGHT: (Direction.UP,),
+    },
+    "\\": {
+        Direction.UP: (Direction.LEFT,),
+        Direction.LEFT: (Direction.UP,),
+        Direction.DOWN: (Direction.RIGHT,),
+        Direction.RIGHT: (Direction.DOWN,),
+    },
+    "|": {
+        Direction.UP: (Direction.UP,),
+        Direction.LEFT: (Direction.UP, Direction.DOWN),
+        Direction.DOWN: (Direction.DOWN,),
+        Direction.RIGHT: (Direction.UP, Direction.DOWN),
+    },
+    "-": {
+        Direction.UP: (Direction.LEFT, Direction.RIGHT),
+        Direction.LEFT: (Direction.LEFT,),
+        Direction.DOWN: (Direction.LEFT, Direction.RIGHT),
+        Direction.RIGHT: (Direction.RIGHT,),
+    },
+    ".": {
+        Direction.UP: (Direction.UP,),
+        Direction.LEFT: (Direction.LEFT,),
+        Direction.DOWN: (Direction.DOWN,),
+        Direction.RIGHT: (Direction.RIGHT,),
+    },
+}
+
+
+@dataclasses.dataclass(frozen=True)
+class Light:
+    pos: Coordinate
+    dir: Direction
+
+
+def calculate_energized_tiles(board: list[str], start_pos: Coordinate, start_dir: Direction) -> int:
+    M, N = len(board), len(board[0])
+    lights = {(start_pos, start_dir)}
+    energized = {start_pos}
+    seen = set()
+    while lights:
+        nxt = set()
+        for coord, dir in lights:
+            if coord.y < 0 or coord.y >= M or coord.x < 0 or coord.x >= N:
+                continue
+            energized.add(coord)
+            tile = board[coord.y][coord.x]
+            for reflection in reflections[tile][dir]:
+                nxt.add((coord.move(reflection), reflection))
+        lights = nxt - seen
+        seen.update(nxt)
+    return len(energized)
+
+
+def part_a(data: str) -> int:
+    board = data.splitlines()
+
+    return calculate_energized_tiles(board, Coordinate.create(0, 0), Direction.RIGHT)
+
+
+def part_b(data: str) -> int:
+    board = data.splitlines()
+    M, N = len(board), len(board[0])
+    top = max(calculate_energized_tiles(board, Coordinate.create(0, x), Direction.DOWN) for x in range(N))
+    bottom = max(calculate_energized_tiles(board, Coordinate.create(M - 1, x), Direction.UP) for x in range(N))
+    left = max(calculate_energized_tiles(board, Coordinate.create(y, 0), Direction.RIGHT) for y in range(M))
+    right = max(calculate_energized_tiles(board, Coordinate.create(y, N - 1), Direction.LEFT) for y in range(M))
+
+    return max((top, bottom, left, right))
+
+    pass
+
+
+if __name__ == "__main__":
+    from aoc_cas.util import solve_with_examples
+
+    solve_with_examples(year=2023, day=16)

tests/fixtures/2023/16.txt

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+.|...\....
+|.-.\.....
+.....|-...
+........|.
+..........
+.........\
+..../.\\..
+.-.-/..|..
+.|....-|.\
+..//.|....
+46
+51