2023: d08: ex2: add solution

2023/d08/ex2/ex2.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+import itertools
+import math
+import sys
+
+Graph = dict[str, list[str]]
+
+
+def solve(input: list[str]) -> int:
+    def parse_graph(input: list[str]) -> Graph:
+        res: Graph = {}
+
+        for line in input:
+            start, dests = line.split(" = ")
+            res[start] = dests[1:-1].split(", ")
+
+        return res
+
+    def parse(input: list[str]) -> tuple[str, Graph]:
+        return input[0], parse_graph(input[2:])
+
+    def navigate(directions: str, graph: Graph, start: str) -> int:
+        pos = start
+        i = 0
+        for dir in itertools.cycle(directions):
+            if pos[-1] == "Z":
+                break
+            pos = graph[pos][0 if dir == "L" else 1]
+            i += 1
+        return i
+
+    directions, graph = parse(input)
+    starts = set(node for node in graph if node[-1] == "A")
+    steps = {navigate(directions, graph, n) for n in starts}
+    return math.lcm(*steps)
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()