150 lines
4.5 KiB
Python
150 lines
4.5 KiB
Python
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#!/usr/bin/env python
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import copy
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import enum
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import sys
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from typing import NamedTuple
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class Point(NamedTuple):
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x: int
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y: int
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class Direction(enum.StrEnum):
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UP = "^"
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RIGHT = ">"
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DOWN = "v"
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LEFT = "<"
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def step(self, p: Point) -> Point:
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dx: int
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dy: int
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match self:
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case Direction.UP:
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dx, dy = -1, 0
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case Direction.RIGHT:
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dx, dy = 0, 1
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case Direction.DOWN:
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dx, dy = 1, 0
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case Direction.LEFT:
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dx, dy = 0, -1
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return Point(p.x + dx, p.y + dy)
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class Object(enum.StrEnum):
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BOX = "O"
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WALL = "#"
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# Maze always contains the left part of the object
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Maze = dict[Point, Object]
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# WideMaze maps left and right side of an object to its (left, right) tuple
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WideMaze = dict[Point, tuple[Point, Point]]
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def solve(input: str) -> int:
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def parse_maze(input: list[str]) -> tuple[Point, Maze]:
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robot: Point | None = None
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maze: Maze = {}
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for x, line in enumerate(input):
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for y, c in enumerate(line):
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if c == ".":
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continue
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if c == "@":
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robot = Point(x, y * 2)
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continue
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maze[Point(x, y * 2)] = Object(c)
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assert robot is not None # Sanity check
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return robot, maze
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def parse_directions(input: str) -> list[Direction]:
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return [Direction(c) for c in input if c in Direction]
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def parse(input: str) -> tuple[Point, Maze, list[Direction]]:
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maze_input, directions_input = input.split("\n\n")
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robot, maze = parse_maze(maze_input.splitlines())
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directions = parse_directions(directions_input)
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return robot, maze, directions
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def step(robot: Point, maze: Maze, d: Direction) -> tuple[Point, Maze]:
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def widen_maze() -> WideMaze:
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res: WideMaze = {}
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for p in maze.keys():
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right_p = Point(p.x, p.y + 1)
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res[p] = (p, right_p)
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res[right_p] = (p, right_p)
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return res
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def boxes_along(wide_maze: WideMaze) -> set[Point] | None:
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def helper(current: Point) -> set[Point] | None:
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# Return empty set if we hit the air
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if current not in wide_maze:
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return set()
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# Query both sides of the object
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left, right = wide_maze[current]
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# Return None if we hit a wall
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if maze[left] == Object.WALL:
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return None
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assert right not in maze # Sanity check
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# Try to move both sides of the box recursively
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res_left: set[Point] = set()
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res_right: set[Point] = set()
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# Only check next_left if not moving right
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if (next_left := d.step(left)) != right:
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if (try_left := helper(next_left)) is None:
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return None
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res_left = try_left
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# And only check next_right if not moving left
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if (next_right := d.step(right)) != left:
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if (try_right := helper(next_right)) is None:
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return None
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res_right = try_right
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# Both sides succeeded, return the set of boxes to move
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return {left} | res_left | res_right
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return helper(d.step(robot))
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def move_boxes(boxes: set[Point]) -> Maze:
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new_maze = copy.copy(maze)
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# Do the move in two steps to avoid overwriting any values during movement
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for box in boxes:
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new_maze.pop(box)
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for box in boxes:
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new_maze[d.step(box)] = maze[box]
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return new_maze
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new_robot = d.step(robot)
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# If we hit a wall, abort the step
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if maze.get(new_robot) == Object.WALL:
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return robot, maze
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# If a box hits a wall, abort the step
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if (boxes := boxes_along(widen_maze())) is None:
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return robot, maze
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# Otherwise move everything along the direction
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return new_robot, move_boxes(boxes)
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def compute_coordinates(maze: Maze) -> int:
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return sum(100 * p.x + p.y for p, obj in maze.items() if obj == Object.BOX)
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robot, maze, directions = parse(input)
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for d in directions:
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robot, maze = step(robot, maze, d)
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return compute_coordinates(maze)
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def main() -> None:
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input = sys.stdin.read()
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print(solve(input))
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if __name__ == "__main__":
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main()
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