aoc

Advent of Code
git clone https://git.pngu.org/aoc
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15_2020.py (433B)

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import fileinput
import re

S = [14, 8, 16, 0, 1, 17]
last_index = {}

for i, n in enumerate(S):
    if i != len(S) - 1:
        last_index[n] = i

while len(S) < 30000000:
    prev = S[-1]
    prev_prev = last_index.get(prev, -1)
    last_index[prev] = len(S) - 1
    if prev_prev == -1:
        next_ = 0
    else:
        next_ = len(S) - 1 - prev_prev
    S.append(next_)
    if len(S) == 2020:
        print(next_)
print(S[-1])