2019: d10: ex1: add solution

2019/d10/ex1/ex1.py

@@ -0,0 +1,81 @@
+#!/usr/bin/env python
+
+import sys
+from itertools import chain
+from math import gcd
+from typing import Set, Tuple
+
+Position = Tuple[int, int]
+
+
+def main() -> None:
+    asteroids = [[c == "#" for c in line.rstrip()] for line in sys.stdin.readlines()]
+
+    def count_spotted(i: int, j: int) -> int:
+        def is_valid(pos: Position) -> bool:
+            return 0 <= pos[0] < len(asteroids) and 0 <= pos[1] < len(asteroids[0])
+
+        def pos_around(radius: int) -> Set[Position]:
+            return set(
+                chain(
+                    filter(
+                        is_valid,
+                        (
+                            (i - offset, j - radius)
+                            for offset in range(-radius, radius + 1)
+                        ),
+                    ),
+                    filter(
+                        is_valid,
+                        (
+                            (i - offset, j + radius)
+                            for offset in range(-radius, radius + 1)
+                        ),
+                    ),
+                    filter(
+                        is_valid,
+                        (
+                            (i - radius, j - offset)
+                            for offset in range(-radius, radius + 1)
+                        ),
+                    ),
+                    filter(
+                        is_valid,
+                        (
+                            (i + radius, j - offset)
+                            for offset in range(-radius, radius + 1)
+                        ),
+                    ),
+                )
+            )
+
+        seen: Set[Position] = set()
+        ans = 0
+        radius = 1
+        while asteroids[i][j]:  # Only do this if are on an asteroid
+            to_visit = pos_around(radius)
+            radius += 1
+            if len(to_visit) == 0:
+                break
+            for pos in to_visit:
+                if not asteroids[pos[0]][pos[1]]:
+                    continue  # No asteroid there
+                rel = (pos[0] - i, pos[1] - j)
+                common = gcd(*rel)
+                rel = (rel[0] // common, rel[1] // common)
+                if rel in seen:
+                    continue  # Already have an asteroid on this path
+                seen.add(rel)
+                ans += 1
+        return ans
+
+    ans, y, x = max(
+        (count_spotted(i, j), i, j)
+        for i in range(len(asteroids))
+        for j in range(len(asteroids[0]))
+    )
+    print(f"({x}, {y}): {ans}")
+
+
+if __name__ == "__main__":
+    main()