2023: d13: ex2: add solution

2023/d13/ex2/ex2.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python
+
+import sys
+from typing import NamedTuple, Optional
+
+
+class Point(NamedTuple):
+    x: int
+    y: int
+
+
+class Grid(NamedTuple):
+    points: set[Point]
+    lines: int
+    rows: int
+
+
+def solve(input: str) -> int:
+    def parse_grid(grid: list[str]) -> Grid:
+        points: set[Point] = set()
+
+        for x, line in enumerate(grid):
+            for y, c in enumerate(line):
+                if c != "#":
+                    continue
+                points.add(Point(x, y))
+
+        return Grid(points, len(grid), len(grid[0]))
+
+    def parse(input: str) -> list[Grid]:
+        return [parse_grid(grid.splitlines()) for grid in input.split("\n\n")]
+
+    def reflect_vertical(grid: Grid) -> Optional[int]:
+        def try_row(row: int) -> set[Point]:
+            smudges: set[Point] = set()
+            for y in range(min(row, grid.rows - row)):
+                for x in range(grid.lines):
+                    left = Point(x, row - y - 1) in grid.points
+                    right = Point(x, row + y) in grid.points
+                    if left and right:
+                        continue
+                    if left or right:
+                        smudges.add(Point(x, row - y - 1))
+            return smudges
+
+        for row in range(1, grid.rows):
+            if len(try_row(row)) == 1:
+                return row
+        return None
+
+    def reflect_horizontal(grid: Grid) -> Optional[int]:
+        def try_line(line: int) -> set[Point]:
+            smudges: set[Point] = set()
+            for x in range(min(line, grid.lines - line)):
+                for y in range(grid.rows):
+                    up = Point(line - x - 1, y) in grid.points
+                    down = Point(line + x, y) in grid.points
+                    if up and down:
+                        continue
+                    if up or down:
+                        smudges.add(Point(line - x - 1, y))
+            return smudges
+
+        for line in range(1, grid.lines):
+            if len(try_line(line)) == 1:
+                return line
+        return None
+
+    def solve(grid: Grid) -> int:
+        if (columns := reflect_vertical(grid)) is not None:
+            return columns
+        if (rows := reflect_horizontal(grid)) is not None:
+            return 100 * rows
+        assert False  # Sanity check
+
+    grids = parse(input)
+    return sum(map(solve, grids))
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()