day15.py

#!/usr/bin/env python3

from collections import defaultdict

src = open("input.txt", "r").read()

# src = "0,3,6"
# src = "3,1,2"

src = [int(x) for x in src.split(",")]

t = len(src)
last = src[-1]

positions = defaultdict(list)

for i, v in enumerate(src):
    positions[v].append(i)


def turn():
    global t, last

    if len(positions[last]) == 1:
        last = 0
    else:
        pos = t - positions[last][-1] - 1
        pos2 = t - positions[last][-2] - 1

        last = pos2 - pos

    positions[last].append(t)

    t += 1


while t < 30000000:
    if t % 10000 == 0:
        print(t)
    turn()

print("answer", t, last)