Advent of Code 2015 Day 18

— Day 18: Like a GIF For Your Yard —

In your grid of 100x100 lights, given your initial configuration, how many lights are on after 100 steps?

import numpy as np
import copy

with open('data-2015-18.txt', 'r') as f:
    inp = f.read().splitlines()

Arrays are a good choice

lites_list = [list(x) for x in inp]

lites_grid = np.array(lites_list)

lites = np.full((102, 102), '.')

lites[1:101,1:101] = lites_grid

Now, let’s iterate!

for s in range(100):
    # lights previously
    lp = copy.deepcopy(lites)
    for x in range(1, 101):
        for y in range(1, 101):
            if lp[x,y] == '.':
                # we might turn on
                if np.sum(np.char.count(lp[x-1:x+2,y-1:y+2], '#')
                ) - np.sum(np.char.count(lp[x,y], '#')) == 3:
                    lites[x,y] = '#'
                else: 
                    lites[x,y] = '.'
            else: 
                # we might turn off
                if np.sum(np.char.count(lp[x-1:x+2,y-1:y+2], '#')
                ) - np.sum(np.char.count(lp[x,y], '#')) in [2,3]:
                    lites[x,y] = '#'
                else: 
                    lites[x,y] = '.'


np.sum(np.char.count(lites[:], '#'))

# 768 

np.int64(768)

— Part Two —

In your grid of 100x100 lights, given your initial configuration, but with the four corners always in the on state, how many lights are on after 100 steps?

for s in range(100):
    # lights previously
    lp = copy.deepcopy(lites)
    for x in range(1, 101):
        for y in range(1, 101):
            if x in [1,100] and y in [1,100]:
                lites[x,y] = '#'
            elif lp[x,y] == '.':
                # we might turn on
                if np.sum(np.char.count(lp[x-1:x+2,y-1:y+2], '#')
                ) - np.sum(np.char.count(lp[x,y], '#')) == 3:
                    lites[x,y] = '#'
                else: 
                    lites[x,y] = '.'
            else: 
                # we might turn off
                if np.sum(np.char.count(lp[x-1:x+2,y-1:y+2], '#')
                ) - np.sum(np.char.count(lp[x,y], '#')) in [2,3]:
                    lites[x,y] = '#'
                else: 
                    lites[x,y] = '.'


np.sum(np.char.count(lites[:], '#'))

# 781

np.int64(597)