Solve day 11 puzzles

Author: coocos

aoc/day11/input.txt

@@ -0,0 +1,10 @@
+7612648217
+7617237672
+2853871836
+7214367135
+1533365614
+6258172862
+5377675583
+5613268278
+8381134465
+3445428733

aoc/day11/puzzle.py

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+from collections import deque
+from typing import Iterable
+from pathlib import Path
+
+Grid = list[list[int]]
+Point = tuple[int, int]
+
+
+def parse_input() -> Grid:
+    return [
+        [int(col) for col in row]
+        for row in (Path(__file__).parent / "input.txt").read_text().splitlines()
+    ]
+
+
+def neighbours(point: Point, grid: Grid) -> Iterable[Point]:
+
+    for x, y in [
+        (0, -1),
+        (1, -1),
+        (1, 0),
+        (1, 1),
+        (0, 1),
+        (-1, 1),
+        (-1, 0),
+        (-1, -1),
+    ]:
+        nx = point[0] + x
+        ny = point[1] + y
+        if not 0 <= nx < len(grid):
+            continue
+        if not 0 <= ny < len(grid):
+            continue
+        yield (nx, ny)
+
+
+def solve() -> None:
+    grid = parse_input()
+    flashes = 0
+    flashes_at_step = []
+
+    while True:
+
+        need_to_flash = deque()
+
+        for y in range(len(grid)):
+            for x in range(len(grid[y])):
+                grid[y][x] += 1
+                if grid[y][x] > 9:
+                    need_to_flash.append((x, y))
+
+        flashed = set()
+        while need_to_flash:
+            x, y = need_to_flash.popleft()
+            if (x, y) in flashed:
+                continue
+            flashed.add((x, y))
+            for nx, ny in neighbours((x, y), grid):
+                grid[ny][nx] += 1
+                if grid[ny][nx] > 9 and (nx, ny) not in flashed:
+                    need_to_flash.append((nx, ny))
+        flashes += len(flashed)
+        flashes_at_step.append(flashes)
+
+        for y in range(len(grid)):
+            for x in range(len(grid[y])):
+                if grid[y][x] > 9:
+                    grid[y][x] = 0
+
+        if len(flashed) == len(grid) ** 2:
+            break
+
+    # First part
+    assert flashes_at_step[100] == 1739
+
+    # Second part
+    assert len(flashes_at_step) == 324
+
+
+if __name__ == "__main__":
+    solve()