import itertools import sys from collections import defaultdict Directions = list[ tuple[ str, tuple[int, int], tuple[tuple[int, int], tuple[int, int], tuple[int, int]] ] ] # (Y, X) DIRECTIONS: Directions = [ ("N", (-1, 0), ((-1, -1), (-1, 0), (-1, 1))), ("S", (1, 0), ((1, -1), (1, 0), (1, 1))), ("W", (0, -1), ((-1, -1), (0, -1), (1, -1))), ("E", (0, 1), ((-1, 1), (0, 1), (1, 1))), ] def min_max_yx(positions: set[tuple[int, int]]) -> tuple[int, int, int, int]: ys, xs = {y for y, x in positions}, {x for y, x in positions} return min(ys), min(xs), max(ys), max(xs) def print_positions(positions: set[tuple[int, int]]): min_y, min_x, max_y, max_x = min_max_yx(positions) print( "\n".join( "".join( "#" if (y, x) in positions else "." for x in range(min_x - 1, max_x + 2) ) for y in range(min_y - 1, max_y + 2) ) ) def round( positions: set[tuple[int, int]], directions: Directions, ): to_move: dict[tuple[int, int], list[tuple[int, int]]] = defaultdict(lambda: []) for y, x in positions: elves = { (dy, dx): (y + dy, x + dx) in positions for dy, dx in itertools.product((-1, 0, 1), (-1, 0, 1)) if (dy, dx) != (0, 0) } if not any(elves.values()): to_move[y, x].append((y, x)) continue found: str | None = None for d, (dy, dx), d_yx_check in directions: if not any(elves[dy, dx] for dy, dx in d_yx_check): found = d to_move[y + dy, x + dx].append((y, x)) break if found is None: to_move[y, x].append((y, x)) positions.clear() for ty, tx in to_move: if len(to_move[ty, tx]) > 1: positions.update(to_move[ty, tx]) else: positions.add((ty, tx)) directions.append(directions.pop(0)) POSITIONS = { (i, j) for i, row in enumerate(sys.stdin.read().splitlines()) for j, col in enumerate(row) if col == "#" } # === part 1 === p1, d1 = POSITIONS.copy(), DIRECTIONS.copy() for r in range(10): round(p1, d1) min_y, min_x, max_y, max_x = min_max_yx(p1) answer_1 = sum( (y, x) not in p1 for y in range(min_y, max_y + 1) for x in range(min_x, max_x + 1) ) print(f"answer 1 is {answer_1}") # === part 2 === p2, d2 = POSITIONS.copy(), DIRECTIONS.copy() answer_2 = 0 while True: answer_2 += 1 backup = p2.copy() round(p2, d2) if backup == p2: break print(f"answer 2 is {answer_2}")