AOC2020D09.py

from itertools import combinations

def get_puzzle_input(a_file_name: str) -> list[int]:
    with open(a_file_name) as INFILE:
        return [int(line) for line in INFILE]

def solve_p1(a_numbers: list[int], a_rolling_window_length: int) -> int:
    current_index = a_rolling_window_length

    while True:
        sum_matches_number: bool = False

        for combo in combinations(numbers[current_index - a_rolling_window_length:current_index], 2):
            if combo[0] + combo[1] == numbers[current_index]:
                sum_matches_number = True
                break

        if sum_matches_number:
            current_index += 1
        else:
            return numbers[current_index]

def solve_p2(a_numbers: list[int], a_target: int) -> tuple[int, int]:
    start_index: int = 0
    current_index: int = start_index
    candidate_numbers: list[int] = []

    while True:
        candidate_numbers.append(a_numbers[current_index])

        if sum(candidate_numbers) == a_target:
            break
        elif sum(candidate_numbers) > a_target:
            start_index += 1
            current_index = start_index
            candidate_numbers = []
            continue
        else:
            current_index += 1

    return min(candidate_numbers), max(candidate_numbers)

numbers = get_puzzle_input('aoc_2020/aoc_2020_day_09.txt')
# print(f"{numbers=}")

p1: int = solve_p1(numbers, 25)
print(f"{p1=}")

p2_lo, p2_hi = solve_p2(numbers, p1)
print(f"p2={p2_lo + p2_hi}")