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@@ -0,0 +1,97 @@
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+#!/usr/bin/env python3
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+import sys
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+from collections import defaultdict
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+
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+def read_grid(f):
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+ lines = [line.replace('\n', '') for line in f]
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+ return tuple(x == '#' for line in lines for x in line), len(lines[0])
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+
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+def evolve_simple(grid, w):
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+ h = len(grid) // w
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+
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+ def adjacent(i):
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+ y, x = divmod(i, w)
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+ nb = 0
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+ if x > 0:
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+ nb += grid[i - 1]
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+ if x < w - 1:
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+ nb += grid[i + 1]
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+ if y > 0:
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+ nb += grid[i - w]
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+ if y < h - 1:
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+ nb += grid[i + w]
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+ return nb
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+
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+ def die_or_infest(i, bug):
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+ return adjacent(i) == 1 if bug else 1 <= adjacent(i) <= 2
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+
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+ return tuple(die_or_infest(i, bug) for i, bug in enumerate(grid))
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+
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+def find_recurring(grid, w):
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+ seen = set()
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+ while grid not in seen:
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+ seen.add(grid)
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+ grid = evolve_simple(grid, w)
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+ return grid
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+
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+def biodiversity(grid):
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+ return sum(bug << i for i, bug in enumerate(grid))
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+
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+def evolve_infinite(grid, w, minutes):
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+ l = len(grid)
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+ assert l == w * w
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+ mid = w // 2 * w + w // 2
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+
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+ top_edge = tuple(range(w))
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+ bottom_edge = tuple(range(l - w, l))
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+ left_edge = tuple(range(0, l, w))
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+ right_edge = tuple(range(w - 1, l, w))
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+
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+ def spread(x, y, nx, ny, level):
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+ ni = ny * w + nx
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+ if ni == mid:
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+ if x > nx:
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+ return right_edge, level + 1
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+ elif x < nx:
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+ return left_edge, level + 1
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+ elif y > ny:
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+ return bottom_edge, level + 1
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+ elif y < ny:
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+ return top_edge, level + 1
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+ elif nx == -1:
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+ return (mid - 1,), level - 1
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+ elif nx == w:
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+ return (mid + 1,), level - 1
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+ elif ny == -1:
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+ return (mid - w,), level - 1
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+ elif ny == w:
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+ return (mid + w,), level - 1
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+ else:
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+ return (ni,), level
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+
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+ def neighbors(i, level):
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+ y, x = divmod(i, w)
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+ yield spread(x, y, x - 1, y, level)
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+ yield spread(x, y, x + 1, y, level)
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+ yield spread(x, y, x, y - 1, level)
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+ yield spread(x, y, x, y + 1, level)
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+
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+ def evolve(bugs):
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+ adjacent = defaultdict(int)
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+ for i, level in bugs:
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+ y, x = divmod(i, w)
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+ for nbs, nblev in neighbors(i, level):
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+ for nb in nbs:
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+ adjacent[(nb, nblev)] += 1
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+ return {x for x, a in adjacent.items()
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+ if a == 1 or (a == 2 and x not in bugs)}
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+
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+ bugs = {(i, 0) for i, bug in enumerate(grid) if bug}
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+ while minutes > 0:
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+ bugs = evolve(bugs)
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+ minutes -= 1
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+ return len(bugs)
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+
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+grid, w = read_grid(sys.stdin)
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+print(biodiversity(find_recurring(grid, w)))
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+print(evolve_infinite(grid, w, 200))
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Taddeus Kroes