2025: d11: ex1: add solution

2025/d11/ex1/ex1.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+
+import functools
+import sys
+
+
+def solve(input: list[str]) -> int:
+    def parse(input: list[str]) -> dict[str, set[str]]:
+        return {
+            dev: set(outputs.split(" "))
+            for dev, outputs in map(lambda s: s.split(": "), input)
+        }
+
+    def count_paths(graph: dict[str, set[str]], start: str, end: str) -> int:
+        @functools.cache
+        def rec(start: str, end: str) -> int:
+            if start == end:
+                return 1
+            return sum(rec(n, end) for n in graph[start])
+
+        # Input is assured to be a DAG, so a simple recursive count is enough
+        return rec(start, end)
+
+    graph = parse(input)
+    return count_paths(graph, "you", "out")
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()