2025: d07: ex2: add solution

2025/d07/ex2/ex2.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python
+
+import functools
+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 count_timelines(start: Point, splitters: set[Point]) -> int:
+        max_x = max(p.x for p in splitters)
+
+        @functools.cache
+        def rec(p: Point) -> int:
+            if p.x > max_x:
+                return 1
+            if p not in splitters:
+                return rec(Point(p.x + 1, p.y))
+            return rec(Point(p.x + 1, p.y - 1)) + rec(Point(p.x + 1, p.y + 1))
+
+        return rec(start)
+
+    start, splitters = parse(input)
+    return count_timelines(start, splitters)
+
+
+def main() -> None:
+    input = sys.stdin.read().splitlines()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()