2019: d12: ex2: add solution

2019/d12/ex2/ex2.py

@@ -0,0 +1,77 @@
+#!/usr/bin/env python
+
+
+import re
+import sys
+from copy import deepcopy
+from dataclasses import dataclass
+from math import gcd
+from typing import List
+
+
+@dataclass
+class Position:
+    x: int
+    y: int
+    z: int
+
+
+def line_to_pos(l: str) -> Position:
+    "<x=4, y=1, z=1>"
+    regex = r"<x=(?P<x>[^,]*), y=(?P<y>[^,]*), z=(?P<z>[^,]*)>"
+    match = re.search(regex, l)
+    assert match is not None  # Sanity check
+    return Position(*(int(match.group(g)) for g in ("x", "y", "z")))
+
+
+def lcm(a: int, b: int, c: int) -> int:
+    def lcm_2(a: int, b: int) -> int:
+        return abs(a * b) // gcd(a, b)
+
+    return lcm_2(lcm_2(a, b), c)
+
+
+def main() -> None:
+    asteroids = [line_to_pos(line) for line in sys.stdin.readlines()]
+    velocities = [Position(0, 0, 0) for __ in asteroids]
+
+    cycles: List[int] = []
+    for attr in ("x", "y", "z"):
+        all_prev_pos = [deepcopy(asteroids)]
+        all_prev_vel = [deepcopy(velocities)]
+        i = 0
+
+        found = False
+        while not found:
+            i += 1
+            for orig, v in zip(asteroids, velocities):
+                for other in asteroids:
+                    if orig.x != other.x:
+                        v.x += 1 if orig.x < other.x else -1
+                    if orig.y != other.y:
+                        v.y += 1 if orig.y < other.y else -1
+                    if orig.z != other.z:
+                        v.z += 1 if orig.z < other.z else -1
+
+            for asteroid, v in zip(asteroids, velocities):
+                asteroid.x += v.x
+                asteroid.y += v.y
+                asteroid.z += v.z
+
+            for old_pos, old_vel in zip(all_prev_pos, all_prev_vel):
+                if all(
+                    n.__getattribute__(attr) == o.__getattribute__(attr)
+                    for n, o in zip(asteroids, old_pos)
+                ) and all(
+                    n.__getattribute__(attr) == o.__getattribute__(attr)
+                    for n, o in zip(velocities, old_vel)
+                ):
+                    found = True
+
+        cycles.append(i)
+
+    print(lcm(*cycles))
+
+
+if __name__ == "__main__":
+    main()