My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Optimize 2017/day21.py
After 3 iterations, a 3x3 grid is transformed into a 9x9 grid, whose
component 3x3 grids can be treated separately from that point on.
Instead of building the full grid (which grows exponentially), store a
count of each 3x3 "subgrid" and operate on each of them independently.
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2017/day21.py
+51
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2017/day21.py
···
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import fileinput
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from collections import Counter
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from utils import new_table
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def lit_pixels(grid):
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return sum(sum(c == '#' for c in row) for row in grid)
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GRID = [
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['.', '#', '.'],
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['.', '.', '#'],
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['#', '#', '#'],
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]
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RULES = {}
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···
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grid = rotated
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for i in range(18):
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size = len(GRID[0])
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d = 2 if size % 2 == 0 else 3
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SUBGRIDS = Counter()
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SUBGRIDS['.#...####'] += 1
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for it in range(18):
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# Build up our list of subgrids
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if it % 3 == 0:
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GRIDS = []
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ORIG_GRIDS = []
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for inp in SUBGRIDS:
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GRIDS.append([list(inp[n:n+3]) for n in range(0, 9, 3)])
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ORIG_GRIDS.append(inp)
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NEW_GRIDS = []
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for grid in GRIDS:
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size = len(grid)
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d = 2 if size % 2 == 0 else 3
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new_size = (size // d) * (d + 1)
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new_grid = new_table(None, width=new_size, height=new_size)
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for y in range(size // d):
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for x in range(size // d):
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# Build the string representation of each 2x2 or 3x3 subgrid
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subgrid = ''
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new_size = (size // d) * (d + 1)
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new_grid = new_table(None, width=new_size, height=new_size)
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for k in range(d):
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subgrid += ''.join(grid[y*d + k][x*d:(x+1)*d])
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for y in range(size // d):
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for x in range(size // d):
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# Build the string representation of each 2x2 or 3x3 subgrid
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subgrid = ''
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# Lookup the corresponding rule and populate the new grid
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out = RULES[subgrid]
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for ny in range(d+1):
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for nx in range(d+1):
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new_grid[y*(d+1) + ny][x*(d+1) + nx] = out[ny*(d+1) + nx]
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for k in range(d):
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subgrid += ''.join(GRID[y*d + k][x*d:(x+1)*d])
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NEW_GRIDS.append(new_grid)
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# Lookup the corresponding rule and populate the new grid
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out = RULES[subgrid]
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for ny in range(d+1):
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for nx in range(d+1):
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new_grid[y*(d+1) + ny][x*(d+1) + nx] = out[ny*(d+1) + nx]
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GRIDS = NEW_GRIDS
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GRID = new_grid
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if it in (4, 17):
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num_pixels = sum(lit_pixels(g) * SUBGRIDS[ORIG_GRIDS[i]] for i, g in enumerate(GRIDS))
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print "Lit pixels after {} iterations:".format(it + 1), num_pixels
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if i == 4:
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print "Lit pixels after 5 iterations:", lit_pixels(GRID)
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# Update the count of independent 3x3 subgrids
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if it % 3 == 2:
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next_subgrids = Counter()
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for i, grid in enumerate(GRIDS):
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mult = SUBGRIDS[ORIG_GRIDS[i]]
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for y in range(0, 9, 3):
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for x in range(0, 9, 3):
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key = ''.join(
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''.join(grid[y+n][x:x+3])
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for n in range(3)
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)
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next_subgrids[key] += mult
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print "Lit pixels after 18 iterations:", lit_pixels(GRID)
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SUBGRIDS = next_subgrids