From a7d74dcae6804dc44da9b7470aa44b90ea18dda2 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Fri, 25 Dec 2020 11:39:46 +0100
Subject: [PATCH] 2020: d25: ex1: add solution

---
 2020/d25/ex1/ex1.py | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100755 2020/d25/ex1/ex1.py

diff --git a/2020/d25/ex1/ex1.py b/2020/d25/ex1/ex1.py
new file mode 100755
index 0000000..6e346d5
--- /dev/null
+++ b/2020/d25/ex1/ex1.py
@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from typing import List
+
+
+def step(value: int, subject: int) -> int:
+    value *= subject
+    value %= 20201227
+    return value
+
+
+def solve(raw: List[int]) -> int:
+    value = 1
+
+    for rounds in itertools.count(1):
+        value = step(value, 7)
+        if value == raw[0]:
+            break
+
+    key = 1
+    for __ in range(rounds):
+        key = step(key, raw[1])
+
+    return key
+
+
+def main() -> None:
+    input = [int(line) for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()