From cfb24fc103289fd73d9773b39a6d38d98070f9c9 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Mon, 19 May 2025 21:31:46 +0100
Subject: [PATCH] 2016: d16: ex2: add solution

---
 2016/d16/ex2/ex2.py | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100755 2016/d16/ex2/ex2.py

diff --git a/2016/d16/ex2/ex2.py b/2016/d16/ex2/ex2.py
new file mode 100755
index 0000000..74e27ee
--- /dev/null
+++ b/2016/d16/ex2/ex2.py
@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+
+
+def solve(input: str) -> str:
+    def curve_step(input: str) -> str:
+        b = input.translate(str.maketrans("01", "10"))[::-1]
+        return input + "0" + b
+
+    def checksum(state: str) -> str:
+        while len(state) % 2 == 0:
+            state = "".join(str(int(a == b)) for a, b in itertools.batched(state, 2))
+        return state
+
+    state = input.strip()
+    disk_size = 35651584
+    while len(state) < disk_size:
+        state = curve_step(state)
+    return checksum(state[:disk_size])
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()