feat: aoc 2025 day 4 solution + tests

Author: Mallory Brickerd

_2025/solutions/day04.py

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+"""Day 4: Printing Department
+
+This module provides the solution for Advent of Code 2025 - Day 4.
+
+It processes a grid of paper rolls to determine which are accessible based
+on the number of adjacent rolls. A roll is accessible if it has fewer than
+four neighbors.
+
+The module contains a Solution class to calculate the number of initially
+accessible rolls (Part 1) and the total number of rolls that can be removed
+iteratively (Part 2).
+"""
+
+from typing import ClassVar
+
+from aoc.models.base import SolutionBase
+
+
+class Solution(SolutionBase):
+    """Determine accessible and removable paper rolls from a grid layout.
+
+    This solution scans a grid representing paper roll locations ('@'). A roll
+    is deemed accessible if it has fewer than four adjacent rolls (including
+    diagonals).
+
+    Part 1 counts the number of rolls that are initially accessible.
+    Part 2 simulates the process of removing all accessible rolls, re-evaluating
+    accessibility, and repeating until no more rolls can be removed, counting
+    the total number of removed rolls.
+    """
+
+    DIRECTIONS: ClassVar[list[tuple[int, int]]] = [
+        (-1, -1),  # up-left
+        (-1, 0),  # up
+        (-1, 1),  # up-right
+        (0, -1),  # left
+        (0, 1),  # right
+        (1, -1),  # down-left
+        (1, 0),  # down
+        (1, 1),  # down-right
+    ]
+
+    def find_open_spaces(self, grid: list[list[str]], rows: int, cols: int) -> list[tuple[int, int]]:
+        """Find all accessible paper rolls in the current grid.
+
+        An accessible roll is one marked '@' with fewer than four adjacent '@' rolls.
+
+        Args:
+            grid: The current grid of paper rolls and empty spaces.
+            rows: The number of rows in the grid.
+            cols: The number of columns in the grid.
+
+        Returns
+        -------
+            list[tuple[int, int]]: A list of (row, col) coordinates for accessible rolls.
+        """
+        positions = []
+        for r in range(rows):
+            for c in range(cols):
+                if grid[r][c] != "@":
+                    continue
+
+                count = 0
+                for dr, dc in self.DIRECTIONS:
+                    nr = r + dr
+                    nc = c + dc
+                    if 0 <= nr < rows and 0 <= nc < cols and grid[nr][nc] == "@":
+                        count += 1
+
+                if count < 4:
+                    positions.append((r, c))
+
+        return positions
+
+    def part1(self, data: list[str]) -> int:
+        """Count the number of paper rolls that are initially accessible.
+
+        This method parses the input grid and counts how many paper rolls ('@')
+        have fewer than four adjacent rolls.
+
+        Args:
+            data: A list of strings representing the grid layout.
+
+        Returns
+        -------
+            int: The total number of initially accessible paper rolls.
+        """
+        grid = [list(row) for row in data]
+        rows, cols = len(grid), len(grid[0])
+        return len(self.find_open_spaces(grid, rows, cols))
+
+    def part2(self, data: list[str]) -> int:
+        """Count the total number of rolls that can be removed.
+
+        This method simulates the iterative removal of accessible paper rolls.
+        In each step, it finds all accessible rolls, adds them to a total count,
+        removes them from the grid (by changing '@' to '.'), and then repeats
+        the process until no more rolls are accessible.
+
+        Args:
+            data: A list of strings representing the initial grid layout.
+
+        Returns
+        -------
+            int: The total number of paper rolls that can be removed.
+        """
+        grid = [list(row) for row in data]
+        rows, cols = len(grid), len(grid[0])
+        positions = self.find_open_spaces(grid, rows, cols)
+
+        count = 0
+        while (c := len(positions)) > 0:
+            count += c
+            for y, x in positions:
+                grid[y][x] = "."
+
+            positions = self.find_open_spaces(grid, rows, cols)
+
+        return count

_2025/tests/data/day04/test_01_input.txt

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+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.

_2025/tests/data/day04/test_02_input.txt

@@ -0,0 +1,10 @@
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.

_2025/tests/test_04.py

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+"""Test suite for Advent of Code daily challenge solution.
+
+This module contains the test cases for the solution to the Advent of Code
+daily puzzle. It uses the TestSolutionUtility to run tests for both parts
+of the challenge.
+
+The template provides a structure for defining tests for a specific day's
+solution, ensuring that the implementation meets the expected outputs for
+given test inputs.
+"""
+from aoc.models.tester import TestSolutionUtility
+
+def test_day04_part1() -> None:
+    """Test the solution for Part 1 of the daily puzzle.
+
+    This test runs the solution for Part 1 of the puzzle against the
+    provided test input and compares the result with the expected output.
+    """
+    TestSolutionUtility.run_test(
+        year=2025,
+        day=4,
+        is_raw=False,
+        part_num=1,
+        expected=13,
+    )
+
+def test_day04_part2() -> None:
+    """Test the solution for Part 2 of the daily puzzle.
+
+    This test runs the solution for Part 2 of the puzzle against the
+    provided test input and compares the result with the expected output.
+    """
+    TestSolutionUtility.run_test(
+        year=2025,
+        day=4,
+        is_raw=False,
+        part_num=2,
+        expected=43,
+    )