AoC 2025 Day 4

Author: pareronia

src/main/python/AoC2025_04.py

@@ -0,0 +1,101 @@
+#! /usr/bin/env python3
+#
+# Advent of Code 2025 Day 4
+#
+
+import sys
+
+from aoc.common import InputData
+from aoc.common import SolutionBase
+from aoc.common import aoc_samples
+from aoc.geometry import Direction
+from aoc.grid import Cell
+
+Input = InputData
+Output1 = int
+Output2 = int
+
+
+TEST = """\
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.
+"""
+
+
+class Solution(SolutionBase[Input, Output1, Output2]):
+    def parse_input(self, input_data: InputData) -> Input:
+        return input_data
+
+    def part_1(self, inputs: Input) -> Output1:
+        grid = list(inputs)
+        ans = 0
+        for r, row in enumerate(grid):
+            for c, ch in enumerate(row):
+                if ch == "@":
+                    cnt = 0
+                    cell = Cell(r, c)
+                    for d in Direction.octants():
+                        n = cell.at(d)
+                        if (
+                            0 <= n[0] < len(grid)
+                            and 0 <= n[1] < len(row)
+                            and grid[n[0]][n[1]] == "@"
+                        ):
+                            cnt += 1
+                    if cnt < 4:
+                        ans += 1
+        return ans
+
+    def part_2(self, inputs: Input) -> Output2:
+        grid = [list(row) for row in inputs]
+        ans = 0
+        while True:
+            new_grid = [list(row) for row in grid]
+            for r, row in enumerate(grid):
+                for c, ch in enumerate(row):
+                    if ch == "@":
+                        cnt = 0
+                        cell = Cell(r, c)
+                        for d in Direction.octants():
+                            n = cell.at(d)
+                            if (
+                                0 <= n[0] < len(grid)
+                                and 0 <= n[1] < len(row)
+                                and grid[n[0]][n[1]] == "@"
+                            ):
+                                cnt += 1
+                        if cnt < 4:
+                            new_grid[r][c] = "."
+                            ans += 1
+            if new_grid == grid:
+                break
+            grid = new_grid
+        return ans
+
+    @aoc_samples(
+        (
+            ("part_1", TEST, 13),
+            ("part_2", TEST, 43),
+        )
+    )
+    def samples(self) -> None:
+        pass
+
+
+solution = Solution(2025, 4)
+
+
+def main() -> None:
+    solution.run(sys.argv)
+
+
+if __name__ == "__main__":
+    main()