From 2cde2f7d82212a9c4cfc8453920ddec7b2bea5ab Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 11 May 2025 03:57:55 +0100
Subject: [PATCH] 2017: d20: ex2: add solution

---
 2017/d20/ex2/ex2.py | 57 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100755 2017/d20/ex2/ex2.py

diff --git a/2017/d20/ex2/ex2.py b/2017/d20/ex2/ex2.py
new file mode 100755
index 0000000..d451315
--- /dev/null
+++ b/2017/d20/ex2/ex2.py
@@ -0,0 +1,57 @@
+#!/usr/bin/env python
+
+import collections
+import sys
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+    z: int
+
+
+class Particle(NamedTuple):
+    pos: Point
+    vel: Point
+    acc: Point
+
+    @classmethod
+    def from_str(cls, input: str) -> "Particle":
+        p, v, a = input.split(", ")
+        return cls(
+            Point(*map(int, p[3:-1].split(","))),
+            Point(*map(int, v[3:-1].split(","))),
+            Point(*map(int, a[3:-1].split(","))),
+        )
+
+    def tick(self) -> "Particle":
+        pos, vel, acc = self
+        vel = Point(*((v + a) for v, a in zip(vel, acc)))
+        pos = Point(*((p + v) for p, v in zip(pos, vel)))
+        return Particle(pos, vel, acc)
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[Particle]:
+        return [Particle.from_str(line) for line in input.splitlines()]
+
+    def tick(particles: list[Particle]) -> list[Particle]:
+        particles = [p.tick() for p in particles]
+        positions = collections.Counter(p.pos for p in particles)
+        return [p for p in particles if positions[p.pos] == 1]
+
+    particles = parse(input)
+    # Guesstimate that 1000 iterations is enough to process all colisions
+    for _ in range(1000):
+        particles = tick(particles)
+    return len(particles)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()