day21p2.py

lines = open('input21.txt').read().strip().split('\n')

rules = {}
for line in lines:
    i, o = line.split('=>')
    i = tuple([tuple(s) for s in i.strip().split('/')])
    o = tuple([tuple(s) for s in o.strip().split('/')])

    n = len(i)
    def new_coords(r, c, flipped, reverse_r, reverse_c):
        if reverse_r:
            r = n-1-r
        if reverse_c:
            c = n-1-c
        if flipped:
            r,c = c,r
        return i[r][c]
    for flipped in [True,False]:
        for reverse_r in [True,False]:
            for reverse_c in [True,False]:
                ii = tuple([tuple(new_coords(r,c,flipped,reverse_r,reverse_c) for c in range(n)) for r in range(n)])
                rules[ii] = o

pattern = [list('.#.'), list('..#'), list('###')]

for t in range(19):
    n = len(pattern)

    ans = 0
    for r in range(n):
        for c in range(n):
            if pattern[r][c] == '#':
                ans += 1
    print t, ans

    if n%2==0:
        block_size = 2
    else:
        block_size = 3
    assert n%block_size == 0
    new_blocks = []
    for r in range(n/block_size):
        block_row = []
        for c in range(n/block_size):
            block_in = tuple([tuple([pattern[r*block_size+rr][c*block_size+cc] for cc in range(block_size)]) for rr in range(block_size)])
            block_row.append(rules[block_in])
        new_blocks.append(block_row)
    new_n = n/block_size*(block_size+1)
    def from_block(r,c):
        r0, r1 = r/(block_size+1), r%(block_size+1)
        c0, c1 = c/(block_size+1), c%(block_size+1)
        return new_blocks[r0][c0][r1][c1]
    new_pattern = [[from_block(r,c) for c in range(new_n)] for r in range(new_n)]
    pattern = new_pattern