2025: d07: ex1: add solution

2025/d07/ex1/ex1.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python
+
+import sys
+from typing import NamedTuple
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+def solve(input: list[str]) -> int:
+    def parse(input: list[str]) -> tuple[Point, set[Point]]:
+        start: Point | None = None
+        splitters: set[Point] = set()
+        for x, line in enumerate(input):
+            for y, c in enumerate(line):
+                pos = Point(x, y)
+                if c == "S":
+                    start = pos
+                elif c == "^":
+                    splitters.add(pos)
+        assert start is not None
+        return start, splitters
+
+    def run_manifold(start: Point, splitters: set[Point]) -> set[Point]:
+        beams = {start}
+        current_row = {start.y}
+        for x in range(start.x + 1, max(p.x for p in splitters) + 1):
+            next_row: set[int] = set()
+            for y in current_row:
+                p = Point(x, y)
+                beams.add(p)
+                if p not in splitters:
+                    next_row.add(y)
+                    continue
+                for neighbour in (y - 1, y + 1):
+                    beams.add(Point(x, neighbour))
+                    next_row.add(neighbour)
+            current_row = next_row
+        return beams
+
+    start, splitters = parse(input)
+    beams = run_manifold(start, splitters)
+    return len(beams & splitters)
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()