2017: d12: ex1: add solution

2017/d12/ex1/ex1.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+
+import sys
+
+
+def solve(input: str) -> int:
+    def parse_line(input: str) -> tuple[int, set[int]]:
+        origin, others = input.split(" <-> ")
+        return int(origin), {int(n) for n in others.split(", ")}
+
+    def parse(input: str) -> dict[int, set[int]]:
+        return {n: children for n, children in map(parse_line, input.splitlines())}
+
+    def reachable(graph: dict[int, set[int]]) -> int:
+        queue = [0]
+        seen: set[int] = set()
+
+        while queue:
+            n = queue.pop()
+            if n in seen:
+                continue
+            seen.add(n)
+            queue.extend(graph[n])
+
+        return len(seen)
+
+    graph = parse(input)
+    return reachable(graph)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()