Day 08

day08/part2.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+import functools
+
+lines = (x.strip() for x in open("input.txt"))
+
+instructions = tuple(int(char == "R") for char in next(lines))
+next(lines)
+nodes = {line[:3]: (line[7:10], line[12:15]) for line in lines}
+
+
+def get_loop(node: str):
+    cnt = 0
+    while True:
+        for char in instructions:
+            node = nodes[node][char]
+            cnt += 1
+            if node[2] == "Z":
+                return cnt
+
+def lcm(a, b):
+    mul = abs(a * b)
+    while b:
+        a, b = b, a % b
+    return mul // a
+
+curr_nodes = tuple(key for key in nodes.keys() if key[2] == "A")
+loops = map(get_loop, curr_nodes)
+print(functools.reduce(lcm, loops, 1))