Advent of code 2020, Day 14, Python3.9

day15.py

from sys import stdin
from functools import reduce

def play(s,i):
    stor,l = s
    j=i-1-stor.get(l,i-1)
    stor[l]=i-1
    return (stor,j)

I=[int(i) for i in stdin.readline().split(',')]
for t in (2021, 30000001):
    print(
        reduce(play,
               range(len(I)+1,t),
               ({i:turn for turn,i in enumerate(I,1)},
                I[-1]))[1])