day 8

1 files changed, 39 insertions, 0 deletions

diff --git a/8.py b/8.py
new file mode 100644
index 0000000..4e01e3c
--- /dev/null
+++ b/8.py
@@ -0,0 +1,39 @@
+# pyright: strict
+import math
+from collections.abc import Callable
+from itertools import cycle
+from sys import stdin
+
+instructions, tree = stdin.read().rstrip("\n").split("\n\n")
+
+nodes: dict[str, tuple[str, str]] = dict()
+for n in tree.split("\n"):
+    k, v = n.split(" = ")
+    l, r = v.strip("()").split(", ")
+    nodes[k] = (l, r)
+
+
+def solve(
+    nodes: dict[str, tuple[str, str]],
+    start: str,
+    end_cond: Callable[[str], bool],
+    instructions: str,
+) -> int:
+    current = start
+    for n, ins in enumerate(cycle(instructions)):
+        if end_cond(current):
+            return n
+        current = nodes[current][0 if ins == "L" else 1]
+    return 0
+
+
+print(solve(nodes, "AAA", lambda c: c == "ZZZ", instructions))
+print(
+    math.lcm(
+        *(
+            solve(nodes, s, lambda c: c.endswith("Z"), instructions)
+            for s in nodes.keys()
+            if s.endswith("A")
+        )
+    )
+)