aoc2020-day15.py

# read in aoc input
data = open("day15.in").read().strip().split(',')


def solve(match):
    # add starting numbers to dict for tracking
    pdict = {}
    for i, p in enumerate(data):
        pdict[int(p)] = [i + 1]

    # setup tracking variables
    last = int(data[-1])
    turn = len(data)

    while True:
        # increase the turn each iteration
        turn += 1

        # exit if turn matches requested aoc number
        if turn == match + 1:
            break

        # if num was only just spoken
        if len(pdict[last]) == 1:
            pdict[0] = [pdict[0][-1], turn]
            last = 0
        # if num has been spoken before
        else:
            # calculate difference between last spoken turn and current turn
            diff = pdict[last][-1] - pdict[last][0]
            # if diff value not in dict add it
            if diff not in pdict:
                pdict[diff] = [turn]
            # else update list for spoken num
            else:
                pdict[diff] = [pdict[diff][-1], turn]
            last = diff

    return last


print(f'Part 1: {solve(2020)}')
print(f'Part 2: {solve(30000000)}')