Add 2025 day 4 solutions

3 files changed, 97 insertions, 0 deletions

diff --git a/2025/04/.gitignore b/2025/04/.gitignore
new file mode 100644
index 0000000..ffc46fe
--- /dev/null
+++ b/2025/04/.gitignore
@@ -0,0 +1 @@
+puzzle-[12].py
diff --git a/2025/04/Makefile b/2025/04/Makefile
new file mode 100644
index 0000000..0a4e980
--- /dev/null
+++ b/2025/04/Makefile
@@ -0,0 +1 @@
+include ../../Makefiles/py.mk
diff --git a/2025/04/puzzles.py b/2025/04/puzzles.py
new file mode 100644
index 0000000..3558269
--- /dev/null
+++ b/2025/04/puzzles.py
@@ -0,0 +1,95 @@
+#!/usr/bin/python3
+
+import itertools
+from typing import Generator, Iterator, Self, TextIO
+
+
+class Grid:
+	@classmethod
+	def from_file(cls, f: TextIO) -> Self:
+		g = Grid()
+		g._grid = mkmap(
+			[[c for c in l if c != '\n'] for l in f.readlines()])
+		return g
+
+	def in_bounds_p(self, z: complex) -> bool:
+		return (
+			0 <= z.real < len(self._grid[0])
+			and 0 <= z.imag < len(self._grid)
+		)
+
+	def accessablep(self, z: complex) -> bool:
+		return self[z] is not None and self[z] < 4
+
+	def indicies(self) -> Iterator[complex]:
+		return itertools.starmap(complex, itertools.product(
+			range(len(self._grid[0])),
+			range(len(self._grid)),
+		))
+
+	def neighbors(self, z: complex) -> Generator[complex, None, None]:
+		for Δ in (
+			-1-1j, -1, -1+1j,
+			 0-1j,      0+1j,
+			+1-1j, +1, +1+1j,
+		):
+			if self.in_bounds_p(z + Δ):
+				yield z + Δ
+
+	def __getitem__(self, z: complex) -> int | None:
+		return self._grid[int(z.real)][int(z.imag)]
+
+	def __setitem__(self, z: complex, n: int | None) -> None:
+		self._grid[int(z.real)][int(z.imag)] = n
+
+
+def mkmap(xs: list[list[str]]) -> list[list[int]]:
+	def get(pos: complex) -> str:
+		r, i = map(int, (pos.real, pos.imag))
+		if 0 <= r < len(xs[0]) and 0 <= i < len(xs):
+			return xs[r][i]
+		return '.'
+
+	return [
+		[
+			sum(get(complex(i, j) + Δ) == '@' for Δ in [
+				-1-1j, -1, -1+1j,
+				 0-1j,      0+1j,
+				+1-1j, +1, +1+1j,
+			])
+			if get(complex(i, j)) == '@'
+			else None
+			for j in range(len(xs[i]))
+		]
+		for i in range(len(xs))
+	]
+
+
+def main() -> None:
+	with open('input', 'r') as f:
+		grid = Grid.from_file(f)
+
+	if PUZZLE_PART == 1:
+		acc = sum(grid.accessablep(z) for z in grid.indicies())
+	else:
+		acc = 0
+		while True:
+			breakp = True
+			for z in grid.indicies():
+				if not grid.accessablep(z):
+					continue
+				breakp = False
+				acc += 1
+				grid[z] = None
+				for p in grid.neighbors(z):
+					if grid[p] is not None:
+						grid[p] -= 1
+
+			if breakp:
+				break
+
+	print(acc)
+
+
+if __name__ == '__main__':
+	main()