2017: d07: ex1: add solution

2017/d07/ex1/ex1.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python
+
+import sys
+from typing import NamedTuple
+
+
+class ProgramYell(NamedTuple):
+    weight: int
+    children: set[str]
+
+
+Tower = dict[str, ProgramYell]
+
+
+def solve(input: str) -> str:
+    def parse_line(line: str) -> tuple[str, ProgramYell]:
+        name, rest = line.split(" ", 1)
+        weight, rest = rest.split(")")
+        children = set(rest.removeprefix(" -> ").split(", ")) if rest else set()
+        return name, ProgramYell(int(weight[1:]), children)
+
+    def parse(input: str) -> Tower:
+        return {name: yell for name, yell in map(parse_line, input.splitlines())}
+
+    def find_base(tower: Tower) -> str:
+        candidates = set(tower.keys())
+        for yell in tower.values():
+            candidates -= yell.children
+        assert len(candidates) == 1
+        return candidates.pop()
+
+    tower = parse(input)
+    return find_base(tower)
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()