#!/usr/bin/env python import sys from cmath import phase from itertools import groupby from math import gcd, pi from pprint import pprint from typing import NamedTuple, Set, Tuple class Position(NamedTuple): x: int y: int def pos_to_angle_dist(pos: Position) -> Tuple[float, float]: cartesian = complex(*pos) angle = phase(cartesian) if angle < -pi / 2: angle += 2.5 * pi else: angle += pi / 2 return (angle, abs(cartesian)) def main() -> None: asteroids = [ Position(x, y) for y, line in enumerate(sys.stdin.readlines()) for x, c in enumerate(line.rstrip()) if c == "#" ] def count_spotted(x: int, y: int) -> int: seen: Set[Position] = set() ans = 0 radius = 1 while True: def is_r_away(pos: Position) -> bool: return max(abs(pos.x - x), abs(pos.y - y)) == radius to_visit = list(filter(is_r_away, asteroids)) radius += 1 if len(to_visit) == 0: break for pos in to_visit: rel = (pos.x - x, pos.y - y) common = gcd(*rel) rel = Position(*(a // common for a in rel)) if rel in seen: continue # Already have an asteroid on this path seen.add(rel) ans += 1 return ans # We need to find the observatory's position as a prerequisite ans, orig = max((count_spotted(*pos), pos) for pos in asteroids) print(f"({orig.x}, {orig.y}): {ans}") def to_rel(p: Position) -> Position: return Position(*(a - o for (a, o) in zip(p, orig))) angle_dists = sorted( (pos_to_angle_dist(to_rel(p)), p) for p in asteroids if p != orig ) grouped_angle_dists = [ [val[1] for val in group] for __, group in groupby(angle_dists, key=lambda x: x[0][0]) ] def find_n_th(n: int) -> Position: assert 0 < n < len(asteroids) # Sanity check while n >= len(grouped_angle_dists): for group in grouped_angle_dists: group.pop(0) n -= 1 return grouped_angle_dists[n - 1][0] x, y = find_n_th(200) print(x * 100 + y) if __name__ == "__main__": main()