From e0bae5d69b7e7a231b8e859ac600a1e49ae1c4f3 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Fri, 9 May 2025 23:53:28 +0100
Subject: [PATCH] 2017: d15: ex2: add solution

---
 2017/d15/ex2/ex2.py | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100755 2017/d15/ex2/ex2.py

diff --git a/2017/d15/ex2/ex2.py b/2017/d15/ex2/ex2.py
new file mode 100755
index 0000000..17eab8e
--- /dev/null
+++ b/2017/d15/ex2/ex2.py
@@ -0,0 +1,43 @@
+#!/usr/bin/env python
+
+import functools
+import itertools
+import sys
+from collections.abc import Iterator
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> tuple[int, int]:
+        a, b = input.splitlines()
+        return int(a.split()[-1]), int(b.split()[-1])
+
+    def generate(seed: int, factor: int, criteria: int) -> int:
+        while True:
+            seed *= factor
+            seed %= 2147483647
+            if (seed % criteria) == 0:
+                return seed
+
+    def judge(a: int, b: int) -> bool:
+        mask = (1 << 16) - 1
+        return (a & mask) == (b & mask)
+
+    def iter_judgements(seed_a: int, seed_b: int) -> Iterator[bool]:
+        generate_a = functools.partial(generate, factor=16807, criteria=4)
+        generate_b = functools.partial(generate, factor=48271, criteria=8)
+
+        while True:
+            seed_a, seed_b = generate_a(seed_a), generate_b(seed_b)
+            yield judge(seed_a, seed_b)
+
+    seed_a, seed_b = parse(input)
+    return sum(itertools.islice(iter_judgements(seed_a, seed_b), 5000000))
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()