Solve 2020 day 17

2020/17_cubes.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python3
+import sys
+from collections import defaultdict
+
+def parse(f):
+    for y, line in enumerate(f):
+        for x, cube in enumerate(line.rstrip()):
+            if cube == '#':
+                yield x, y, 0, 0
+
+def neighbors(coord, extra_dim):
+    x, y, z, w = coord
+    for dx in (-1, 0, 1):
+        for dy in (-1, 0, 1):
+            for dz in (-1, 0, 1):
+                for dw in (-1, 0, 1) if extra_dim else (0,):
+                    if dx or dy or dz or dw:
+                        yield x + dx, y + dy, z + dz, w + dw
+
+def changes(active, extra_dim):
+    inactive = defaultdict(int)
+    for coord in active:
+        active_nbs = 0
+        for nb in neighbors(coord, extra_dim):
+            if nb in active:
+                active_nbs += 1
+            else:
+                inactive[nb] += 1
+        if active_nbs not in (2, 3):
+            yield coord, False
+
+    for coord, active_nbs in inactive.items():
+        if active_nbs == 3:
+            yield coord, True
+
+def cycle(active, n, extra_dim):
+    active = set(active)
+    for i in range(n):
+        for coord, activate in list(changes(active, extra_dim)):
+            (active.add if activate else active.remove)(coord)
+    return len(active)
+
+active = list(parse(sys.stdin))
+print(cycle(active, 6, False))
+print(cycle(active, 6, True))

2020/input/17

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+.###.###
+.#.#...#
+..##.#..
+..##..##
+........
+##.#.#.#
+..###...
+.####...