Sean McLemon | Advent of Code

2017-12-17 - Spinlock

(original .ipynb)

test_skip = 3
puzzle_skip = 344

def part_one(skip):
    buffer = [0]
    val = 1
    pos = 0

    while val <= 2017:
        pos = (pos + skip) % val + 1
        buffer.insert(pos, val)
        val += 1

    return buffer[pos+1]

assert 638 == part_one(test_skip)

print("part one:", part_one(puzzle_skip))

part one: 996

# realised we actually don't need to build the buffer, just track what we
# _would_ have written to position [1]
def part_two():
    val = 1
    pos = 0
    after_zero = None

    while val <= 50000000:
        pos = (pos + puzzle_skip) % val + 1
        if pos == 1:
            after_zero = val
        val += 1
    
    return after_zero

print("part two:", part_two())

part two: 1898341