advent_of_code/2021/6/6_2.py

#!/usr/bin/env python
# 2021 - Advent Of Code - 6 part 2

def parse_file(file):
    with open(file, encoding="utf-8") as f:
        line = f.readline()

    list_state = [int(x) for x in line.split(',')]

    state = [0] * 9
    for c in range(0, 9):
        state[c] = list_state.count(c)

    return state


def iterate(state):
    new_fish = state[0]
    state[0] = state[1]
    state[1] = state[2]
    state[2] = state[3]
    state[3] = state[4]
    state[4] = state[5]
    state[5] = state[6]
    state[6] = state[7] + new_fish
    state[7] = state[8]
    state[8] = new_fish


# init_state = parse_file('input_example.txt')
init_state = parse_file('input.txt')
print(f'Initial state: {init_state}')

DAYS = 256

for d in range(DAYS):
    iterate(init_state)

print(f'There\'s {sum(init_state)} lanternfish after {DAYS} days')