Solve 2025 day 4

puzzles/solutions/2025/d04/p1.py

@@ -0,0 +1,63 @@
+import itertools
+import sys
+
+example_input = """
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.
+""".strip()
+
+PAPER_ROLL = "@"
+MAX_ADJACENT_PAPER_ROLLS = 3
+
+Grid = list[list[str]]
+Position = tuple[int, int]
+
+
+def get_grid(input_text: str) -> Grid:
+    return [list(line) for line in input_text.splitlines()]
+
+
+def get_adjacent_rolls_number(grid: Grid, row: int, column: int):
+    min_row = max(row - 1, 0)
+    max_row = min(row + 1, len(grid) - 1)
+    min_column = max(column - 1, 0)
+    max_column = min(column + 1, len(grid[0]) - 1)
+    return (
+        sum(
+            grid[current_row][current_column] == PAPER_ROLL
+            for current_row, current_column in itertools.product(
+                range(min_row, max_row + 1), range(min_column, max_column + 1)
+            )
+        )
+        # Exclude the cell we're counting adjacent around.
+        - (grid[row][column] == PAPER_ROLL)
+    )
+
+
+def get_accessible_rolls(grid: Grid) -> list[Position]:
+    return [
+        (row, column)
+        for row, column in itertools.product(range(len(grid)), range(len(grid[0])))
+        if (
+            grid[row][column] == PAPER_ROLL
+            and get_adjacent_rolls_number(grid, row, column) <= MAX_ADJACENT_PAPER_ROLLS
+        )
+    ]
+
+
+def get_answer(input_text: str):
+    grid = get_grid(input_text)
+    return len(get_accessible_rolls(grid))
+
+
+if __name__ == "__main__":
+    puzzle_input = sys.argv[1] if len(sys.argv) > 1 else example_input
+    print(get_answer(puzzle_input))

puzzles/solutions/2025/d04/p2.py

@@ -0,0 +1,29 @@
+import sys
+
+import p1
+
+EMPTY_CELL = "."
+
+
+def clean_accessed_rolls(
+    grid: p1.Grid, accessible_rolls_positions: list[p1.Position]
+) -> None:
+    for row, column in accessible_rolls_positions:
+        grid[row][column] = EMPTY_CELL
+
+
+def get_answer(input_text: str):
+    grid = p1.get_grid(input_text)
+    total_accessible_rolls = 0
+    while True:
+        accessible_rolls = p1.get_accessible_rolls(grid)
+        if not accessible_rolls:
+            break
+        total_accessible_rolls += len(accessible_rolls)
+        clean_accessed_rolls(grid, accessible_rolls)
+    return total_accessible_rolls
+
+
+if __name__ == "__main__":
+    puzzle_input = sys.argv[1] if len(sys.argv) > 1 else p1.example_input
+    print(get_answer(puzzle_input))