Day 20; 2020 is done!

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dece 2020-12-27 18:22:13 +01:00
parent 2a07c6458c
commit 1310c4314e

133
2020/day20.py Normal file
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import math
import sys
DIM = 10
def main():
groups = sys.stdin.read().rstrip().split("\n\n")
tiles = {}
for group in groups:
lines = [line.rstrip() for line in group.splitlines()]
tile_id = int(lines[0][5:].rstrip(":"))
tiles[tile_id] = list(map(list, lines[1:]))
idim = int(math.sqrt(len(tiles)))
# Part 1
# instructions are not very clean, but looks like we only have to check 3
# rotations + optionally horizontal flip. vertical flip is not needed on
# example, and a vflip is actually rot180 + hflip.
perms = {}
for tile_id, tile in tiles.items():
perms[tile_id] = permutations(tile)
image = search({}, 0, 0, [], perms, idim)
tl = image[(0, 0)]
tr = image[(0, idim - 1)]
bl = image[(idim - 1, 0)]
br = image[(idim - 1, idim - 1)]
print("Multiplied corners:", tl[0] * tr[0] * bl[0] * br[0])
# Part 2
pattern = [
(0, 0), (1, 1),
(4, 1), (5, 0), (6, 0), (7, 1),
(10, 1), (11, 0), (12, 0), (13, 1),
(16, 1), (17, 0), (18, 0), (18, -1), (19, 0)
]
merged = merge_tiles(image, perms, idim)
global DIM
DIM = len(merged)
perms = permutations(merged)
max_monsters = max(find_monsters(perm, pattern) for perm in perms)
num_dashes = sum(c == "#" for row in merged for c in row)
monster_dashes = max_monsters * len(pattern)
print("Roughness:", num_dashes - monster_dashes)
def permutations(tile):
return [
tile,
hflip(tile),
rot90(tile),
rot90(hflip(tile)),
rot90(rot90(tile)),
rot90(rot90(hflip(tile))),
rot90(rot90(rot90(tile))),
rot90(rot90(rot90(hflip(tile)))),
]
def rot90(tile):
rtile = [[None for _ in range(DIM)] for _ in range(DIM)]
for x in range(DIM):
for y in range(DIM):
rtile[x][y] = tile[DIM - y - 1][x]
return rtile
def hflip(tile):
return [row[::] for row in tile[::-1]]
def search(image, x, y, placed, perms, idim):
fitting = find_fitting(image, x, y, placed, perms)
if (x, y) == (idim - 1, idim - 1) and len(fitting) == 1:
image[(idim - 1, idim - 1)] = fitting[0]
return image
for fit in fitting:
nimage = image.copy()
nimage[(x, y)] = fit
nx = (x + 1) % idim
ny = y if nx > 0 else y + 1
nplaced = placed + [fit[0]]
if (complete_image := search(nimage, nx, ny, nplaced, perms, idim)):
return complete_image
def find_fitting(image, x, y, placed, perms):
up_perm = image.get((x, y - 1))
up = perms[up_perm[0]][up_perm[1]] if up_perm else None
left_perm = image.get((x - 1, y))
left = perms[left_perm[0]][left_perm[1]] if left_perm else None
down_perm = image.get((x, y + 1))
down = perms[down_perm[0]][down_perm[1]] if down_perm else None
right_perm = image.get((x + 1, y))
right = perms[right_perm[0]][right_perm[1]] if right_perm else None
return [
(tile_id, tile_perm_id)
for tile_id, tile_perms in perms.items()
if tile_id not in placed
for tile_perm_id, tile_perm in enumerate(tile_perms)
if fits(tile_perm, up, left, down, right)
]
def fits(tile, up, left, down, right):
return all((
not up or tile[0] == up[-1],
not down or tile[-1] == down[0],
not left or [r[0] for r in tile] == [r[-1] for r in left],
not right or [r[-1] for r in tile] == [r[0] for r in right],
))
def merge_tiles(image, perms, idim):
tdim = DIM - 2
merged = [[] for _ in range(idim * tdim)]
for ix in range(idim):
for iy in range(idim):
i_tile_id, i_perm_id = image[(ix, iy)]
tile = perms[i_tile_id][i_perm_id]
for y, row in enumerate(tile[1:-1]):
merged[iy * tdim + y] += row[1:-1]
return merged
def find_monsters(image, pattern):
w, h = len(image[0]), len(image)
num_monsters = 0
for x in range(w):
for y in range(h):
for px, py in pattern:
ix, iy = x + px, y + py
if not 0 <= ix < w or not 0 <= iy < h:
break
if image[iy][ix] != "#":
break
else:
num_monsters += 1
return num_monsters
if __name__ == "__main__":
main()