From 9364a582c389843b47540d3b31dd025a7cd1ad9f Mon Sep 17 00:00:00 2001
From: Christoph Stahl <christoph.stahl@uni-dortmund.de>
Date: Fri, 8 Dec 2023 11:42:28 +0100
Subject: [PATCH] solution Day 08

---
 aoc/aoc.py   |  4 ++--
 aoc/day08.py | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 2 deletions(-)
 create mode 100644 aoc/day08.py

diff --git a/aoc/aoc.py b/aoc/aoc.py
index 0da2258..39ea1ff 100644
--- a/aoc/aoc.py
+++ b/aoc/aoc.py
@@ -182,7 +182,7 @@ class AocParseLinesSameParser(Generic[T1], AocParseLines[T1, T1]):
 def run_latest() -> None:
     days = [
         import_module(f".{file.stem}", package="aoc")
-        for file in Path("aoc").iterdir()
+        for file in sorted(Path("aoc").iterdir())
         if file.name.endswith(".py") and file.name.startswith("day")
     ]
     day = days[-1]
@@ -193,7 +193,7 @@ def run_latest() -> None:
 def main() -> None:
     days = [
         import_module(f".{file.stem}", package="aoc")
-        for file in Path("aoc").iterdir()
+        for file in sorted(Path("aoc").iterdir())
         if file.name.endswith(".py") and file.name.startswith("day")
     ]
     for day in days:
diff --git a/aoc/day08.py b/aoc/day08.py
new file mode 100644
index 0000000..bc5a2b7
--- /dev/null
+++ b/aoc/day08.py
@@ -0,0 +1,68 @@
+from __future__ import annotations
+import itertools
+import math
+from typing import Optional
+
+from .aoc import Aoc2, AocSameParser
+
+
+class Map:
+    def __init__(self, inpt: str) -> None:
+        lines = inpt.splitlines()
+
+        self.directions: list[int] = [0 if rl == "L" else 1 for rl in lines[0]]
+
+        self.rules = {line[:3]: (line[7:10], line[12:15]) for line in lines[2:]}
+
+
+class Day08(AocSameParser[Map], Aoc2[Map, Map]):
+    def parseinput(self, inpt: str) -> Map:
+        return Map(inpt)
+
+    def part1(self, inpt: Map) -> int:
+        current = "AAA"
+
+        for steps, direction in enumerate(itertools.cycle(inpt.directions)):
+            if current == "ZZZ":
+                return steps
+            else:
+                current = inpt.rules[current][direction]
+        raise RuntimeError("End of the rainbow")
+
+    def find_loop(self, list_of_nrs: list[int]) -> Optional[tuple[int, int]]:
+        for index in range(len(list_of_nrs)):
+            for index in range(len(list_of_nrs[index + 1 :])):
+                diff = list_of_nrs[index + 1] - list_of_nrs[index]
+                if list_of_nrs[index + 1] + diff in list_of_nrs:
+                    return list_of_nrs[index], diff
+        return None
+
+    def part2(self, inpt: Map) -> int:
+        current = [node for node in inpt.rules.keys() if node.endswith("A")]
+        steps_to_z = [[] for _ in current]
+        loops: list[Optional[tuple[int, int]]] = [None for _ in current]
+
+        for steps, direction in enumerate(itertools.cycle(inpt.directions)):
+            for n, node in enumerate(current):
+                if node.endswith("Z"):
+                    steps_to_z[n].append(steps)
+                loops[n] = self.find_loop(steps_to_z[n])
+
+            if not any(loop is None for loop in loops):
+                break
+            else:
+                current = [inpt.rules[node][direction] for node in current]
+
+        # Turns out, each path directly loops :/
+        return math.lcm(*(loop[0] for loop in loops if loop is not None))
+
+
+def main() -> None:
+    day08 = Day08(2023, 8)
+    day08._example_code_nr1 = 1
+    day08._example_code_nr2 = -1
+    day08.run()
+
+
+if __name__ == "__main__":
+    main()