AOC2021 Day 20 (Python)

day20_tests.py

def read_file(file):
    i = iter(line.strip() for line in file)
    algo = [c == '#' for c in next(i)]

    assert len(algo) == 512
    assert next(i) == ''

    grid = set((x, y) for y, line in enumerate(i) for x, c in enumerate(line) if c == '#')
    return algo, grid


def adjacent(coord):
    x, y = coord
    for ay in range(y - 1, y + 2):
        for ax in range(x - 1, x + 2):
            yield ax, ay


def lookup(algo, grid, outside_is_lit, outer_bounds, coord):
    min_x, max_x, min_y, max_y = outer_bounds

    def is_lit(c):
        if c in grid:
            return True
        if not outside_is_lit:
            return False
        x, y = c
        return x <= min_x or x >= max_x or y<= min_y or y >= max_y

    digits = ('1' if is_lit(a) else '0'
              for a in adjacent(coord))
    lookup_index = int(str.join('', digits), 2)
    return algo[lookup_index]


def bounds(grid):
    min_x = min(x for (x, _) in grid)
    max_x = max(x for (x, _) in grid)
    min_y = min(y for (_, y) in grid)
    max_y = max(y for (_, y) in grid)

    return min_x, max_x, min_y, max_y


def expand_bounds(bounds):
    min_x, max_x, min_y, max_y = bounds
    return min_x - 1, max_x + 1, min_y - 1, max_y + 1


def next_gen(algo, grid, gen_number):
    expanded_bounds = expand_bounds(bounds(grid))
    min_x, max_x, min_y, max_y = expanded_bounds

    outside_is_lit = gen_number % 2 == 1 and algo[0]

    return set((x, y) for x in range(min_x, max_x + 1)
               for y in range(min_y, max_y + 1)
               if lookup(algo, grid, outside_is_lit, expanded_bounds, (x, y)))


def pretty_print(grid):
    min_x, max_x, min_y, max_y = bounds(grid)

    return str.join('\n',
                    (str.join("", ('#' if (x, y) in grid else '.'
                                   for x in range(min_x, max_x + 1)))
                     for y in range(min_y, max_y + 1)))


def test_apply_algo():
    example_algo_str = """
    ..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..##
    #..######.###...####..#..#####..##..#.#####...##.#.#..#.##..#.#......#.###
    .######.###.####...#.##.##..#..#..#####.....#.#....###..#.##......#.....#.
    .#..#..##..#...##.######.####.####.#.#...#.......#..#.#.#...####.##.#.....
    .#..#...##.#.##..#...##.#.##..###.#......#.#.......#.#.#.####.###.##...#..
    ...####.#..#..#.##.#....##..#.####....##...##..#...#......#.#.......#.....
    ..##..####..#...#.#.#...##..#.#..###..#####........#..####......#..#
    """
    example_algo = [c == '#' for c in str.join('', (line.strip() for line in example_algo_str.split('\n')))]

    example_grid_str = """
    #..#.
    #....
    ##..#
    ..#..
    ..###
    """
    example_grid = set((x, y) for y, line in enumerate(example_grid_str.strip().split('\n'))
                       for x, c in enumerate(line.strip()) if c == '#')

    print()
    print(pretty_print(example_grid))

    print()
    print(pretty_print(g2 := next_gen(example_algo, example_grid, 0)))

    print()
    print(pretty_print(g3 := next_gen(example_algo, g2, 1)))

    assert len(g3) == 35

    with open('puzzle_inputs/day20.txt') as file:
        algo, grid = read_file(file)

    print()
    g = grid
    for i in range(2):
        g = next_gen(algo, g, i)

    print()
    print(len(g))
    for i in range(48):
        g = next_gen(algo, g, i)

    print(len(g))