Day 25

2020/day25.py

@@ -0,0 +1,29 @@
+import sys
+
+def main():
+    lines = [line.rstrip() for line in sys.stdin]
+    cpk, dpk = int(lines[0]), int(lines[1])
+
+    dls = crack(dpk, 7)  # cracking door's key is much quicker
+    k = gen_key(cpk, dls)
+    print(k)
+        
+def step(v, sn):
+    return (v * sn) % 20201227
+
+def crack(pk, sn):
+    i = 0
+    v = 1
+    while v != pk:
+        v = step(v, sn)
+        i += 1
+    return i
+
+def gen_key(sn, ls):
+    v = 1
+    for _ in range(ls):
+        v = step(v, sn)
+    return v
+
+if __name__ == "__main__":
+    main()