Part 1



In [5]:

    
initial = '.##..#.#..##..##..##...#####.#.....#..#..##.###.#.####......#.......#..###.#.#.##.#.#.###...##.###.#'



In [6]:

    
r = ! cat input.txt | tr '\n' ';'
r = dict(list(map(lambda x: tuple(x.split(' => ')), r[0].split(';')[:-1])))



In [31]:

    
def evolve(state, rules, time):
    s = state
    for t in range(1, time + 1):
        n = len(s)
        s = '....' + s + '....'
        new = []
        for i in range(n + 5):
            k = s[i: i + 5]
            new.append(rules.get(k, '.'))
        s = ''.join(new)
        yield list(filter(lambda x: s[x + 2 * t] == '#', range(-2 * t, len(state) + 2 * t)))

def sumofpots(state, rules, time):
    final = None
    for l in evolve(state, rules, time):
        final = l
    return sum(final)

Test



In [32]:

    
initial_test = '#..#.#..##......###...###'
rules_test = ! cat input_test.txt | tr '\n' ';'
rules_test = dict(list(map(lambda x: tuple(x.split(' => ')), rules_test[0].split(';')[:-1])))



In [33]:

    
sumofpots(initial_test, rules_test, 20)









    Out[33]:





325

Solution



In [34]:

    
sumofpots(initial, r, 20)









    Out[34]:





3738

Part 2

A pattern is a configuration of plants modulo shifting. Every pattern has the following signature: the sequence of numbers occupied by plants, with respect to the leftmost position which we take as 0.



In [43]:

    
forever = 50000000000



In [62]:

    
def pattern_repetition(state, rules, time):
    hashes = {}
    period = None
    for i, l in enumerate(evolve(state, rules, time)):
        sig = hash(tuple([c - l[0] for c in l]))
        if sig in hashes:
            period = i - hashes[sig]
            break
        hashes[hash(sig)] = i
    return i + 1, period, l



In [65]:

    
generation, period, l = pattern_repetition(initial, r, forever)
generation, period









    Out[65]:





(100, 1)



In [66]:

    
len(l) * (forever - generation) + sum(l)









    Out[66]:





3900000002467