From c641dda28310318af8bd0fa6f72a5e1dbc723dac Mon Sep 17 00:00:00 2001
From: Tom van der Lee <tom@vanderlee.io>
Date: Thu, 4 Dec 2025 17:06:44 +0100
Subject: Added day4

---
 aoc/datastructures.py |  8 ++++++
 day4/__init__.py      | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++
 day4/example.txt      | 10 +++++++
 3 files changed, 90 insertions(+)
 create mode 100644 day4/__init__.py
 create mode 100644 day4/example.txt

diff --git a/aoc/datastructures.py b/aoc/datastructures.py
index 1f141e2..9c9594a 100644
--- a/aoc/datastructures.py
+++ b/aoc/datastructures.py
@@ -30,6 +30,14 @@ class Coordinate(namedtuple("Coordinate", ["x", "y"])):
             py,
         )
 
+    def in_bounds(self, field: list[list]) -> bool:
+        return not (
+            self.x < 0
+            or self.y < 0
+            or self.y > len(field) - 1
+            or self.x > len(field[0]) - 1
+        )
+
     def neighbours(self, no_diagonal: bool = False) -> Iterator["Coordinate"]:
         if no_diagonal:
             yield self + Coordinate(-1, 0)
diff --git a/day4/__init__.py b/day4/__init__.py
new file mode 100644
index 0000000..d52d0a1
--- /dev/null
+++ b/day4/__init__.py
@@ -0,0 +1,72 @@
+# -*- coding: utf-8 -*-
+from abc import ABC
+from typing import Iterator
+
+from aoc import BaseAssignment, I, T
+from aoc.datastructures import Coordinate
+
+
+class Assignment(BaseAssignment, ABC):
+    def parse_item(cls, item: str) -> Iterator[list[str]]:
+        yield [c for c in item]
+
+    @classmethod
+    def check_accessible_coordinate(
+        cls, field: list[list[str]], coordinate: Coordinate
+    ) -> bool:
+        neighbouring_roll_count = 0
+        for neighbor in coordinate.neighbours():
+            if neighbor.in_bounds(field) and field[neighbor.y][neighbor.x] == "@":
+                neighbouring_roll_count += 1
+
+        return neighbouring_roll_count < 4
+
+    @classmethod
+    def get_accessible_coordinates(
+        cls, field: list[list[str]], coordinates: list[Coordinate]
+    ) -> list[Coordinate]:
+        accessible_coordinates = []
+        for coordinate in coordinates:
+            if field[coordinate.y][coordinate.x] != "@":
+                continue
+
+            if cls.check_accessible_coordinate(field, coordinate):
+                accessible_coordinates.append(coordinate)
+
+        return accessible_coordinates
+
+
+class AssignmentOne(Assignment):
+    example_result = 13
+
+    def run(self, input: Iterator[str]) -> int:
+        field = [next(self.parse_item(i)) for i in input]
+
+        coordinates = [
+            Coordinate(x, y) for y in range(len(field)) for x in range(len(field[y]))
+        ]
+
+        return len(self.get_accessible_coordinates(field, coordinates))
+
+
+class AssignmentTwo(Assignment):
+    example_result = 43
+
+    def run(self, input: Iterator[str]) -> int:
+        field = [next(self.parse_item(i)) for i in input]
+
+        coordinates = [
+            Coordinate(x, y) for y in range(len(field)) for x in range(len(field[y]))
+        ]
+
+        rolls_removed = 0
+        while True:
+            accessible_coordinates = self.get_accessible_coordinates(field, coordinates)
+
+            if len(accessible_coordinates) == 0:
+                return rolls_removed
+
+            for coordinate in accessible_coordinates:
+                field[coordinate.y][coordinate.x] = "."
+
+            rolls_removed += len(accessible_coordinates)
diff --git a/day4/example.txt b/day4/example.txt
new file mode 100644
index 0000000..8209399
--- /dev/null
+++ b/day4/example.txt
@@ -0,0 +1,10 @@
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.
-- 
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