2018: d07: ex1: add solution

2018/d07/ex1/ex1.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python
+
+import sys
+from collections import defaultdict
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+def solve(input: str) -> str:
+    def parse(input: list[str]) -> dict[str, set[str]]:
+        graph: dict[str, set[str]] = defaultdict(set)
+        for line in input:
+            split = line.split()
+            prev, after = split[1], split[7]
+            graph[after].add(prev)
+            graph[prev]  # Ensure that all nodes are in the dictionary
+        return graph
+
+    def topo_sort(graph: dict[str, set[str]]) -> list[str]:
+        res: list[str] = []
+
+        queue = {n for n, deps in graph.items() if not deps}
+        seen: set[str] = set()
+
+        while queue:
+            # We must pop in alphabetical order
+            node = min(queue)
+            queue.remove(node)
+
+            res.append(node)
+            seen.add(node)
+
+            # Iterate over all nodes as we don't have information on children
+            for child, deps in graph.items():
+                if child in seen:
+                    continue
+                if deps - seen:
+                    continue
+                queue.add(child)
+
+        return res
+
+    graph = parse(input.splitlines())
+    return "".join(topo_sort(graph))
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()