2020/24

y2020/p24.py

+import collections
+import re
+import sys
+
+
+def calc(pos):
+    is_black = pos in active
+    count = sum(pos + step in active for step in maps.values())
+    if is_black and count not in {1, 2}:
+        return False
+    elif not is_black and count == 2:
+        return True
+    return is_black
+
+
+text = sys.stdin.read()
+maps = {'w': 2, 'e': -2, 'nw': 1+1j, 'ne': -1+1j, 'sw': 1-1j, 'se': -1-1j}
+grid = collections.defaultdict(bool)
+for line in text.splitlines():
+    end = sum(map(maps.get, re.findall(r'(se|sw|nw|ne|e|w)', line)))
+    grid[end] = not grid[end]
+active = {pos for pos in grid if grid[pos]}
+print(len(active))
+
+
+for _ in range(100):
+    active = {p + s for p in active for s in maps.values() if calc(p + s)}
+print(len(active))