From 4b71dee7c440e8bd6192e5b0f72785567da5ab32 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Fri, 11 Dec 2020 08:41:47 +0100
Subject: [PATCH] 2020: d11: ex2: add solution

---
 2020/d11/ex2/ex2.py | 48 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100755 2020/d11/ex2/ex2.py

diff --git a/2020/d11/ex2/ex2.py b/2020/d11/ex2/ex2.py
new file mode 100755
index 0000000..ce8bad5
--- /dev/null
+++ b/2020/d11/ex2/ex2.py
@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+
+import itertools
+import sys
+from copy import deepcopy
+from typing import Iterator, List, Tuple
+
+Grid = List[List[str]]
+
+
+def update(grid: Grid) -> Grid:
+    def neightbours(x: int, y: int) -> Iterator[Tuple[int, int]]:
+        for dx, dy in itertools.product(range(-1, 2), range(-1, 2)):
+            if dx == 0 and dy == 0:
+                continue
+
+            new_x, new_y = x + dx, y + dy
+            while 0 <= new_x < len(grid) and 0 <= new_y < len(grid[0]):
+                if grid[new_x][new_y] in "L#":
+                    yield new_x, new_y
+                    break
+                new_x, new_y = new_x + dx, new_y + dy
+
+    new_grid = deepcopy(grid)
+
+    for x, y in itertools.product(range(len(grid)), range(len(grid[0]))):
+        num_alive = sum(grid[nx][ny] == "#" for nx, ny in neightbours(x, y))
+        if num_alive == 0 and grid[x][y] == "L":
+            new_grid[x][y] = "#"
+        elif num_alive >= 5 and grid[x][y] == "#":
+            new_grid[x][y] = "L"
+
+    return new_grid
+
+
+def solve(grid: Grid) -> int:
+    while (new_grid := update(grid)) != grid:
+        grid = new_grid
+    return sum(sum(pos == "#" for pos in line) for line in grid)
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve([[line[i] for i in range(len(line))] for line in input]))
+
+
+if __name__ == "__main__":
+    main()