AOC 2021 Day 7

# aoc202107.py

# Refactor - this is very slow

import pathlib
import sys


def parse(puzzle_input: str) -> list[int]:
    """ Parse input """
    return [int(n) for n in puzzle_input.split(',')]


def calc_cost(target: int, positions: list[int]) -> int:
    """ Calculate the sum of the differences between target and items in positions """
    cost = 0
    for pos in positions:
        cost += abs(target - pos)
    return cost


def triangular(num: int) -> int:
    """ Return the triangular number for num """
    return (num * (num + 1)) // 2


def calc_new_cost(target: int, positions: list[int]) -> int:
    """ Calculate the sum of the differences between target and items in positions """
    cost = 0
    for pos in positions:
        diff = abs(target - pos)
        cost += triangular(diff)
    return cost


def part1(data: list[int]) -> int:
    """ Solve part 1 """
    freq_positions = range(min(data), max(data))
    return min(calc_cost(n, data) for n in freq_positions)


def part2(data: list[int]) -> int:
    """ Solve part 2 """
    freq_positions = range(min(data), max(data))
    return min(calc_new_cost(n, data) for n in freq_positions)


def solve(puzzle_input: str) -> tuple[int, int]:
    """ Solve the puzzle for the given input """
    data = parse(puzzle_input)
    solution1 = part1(data)  # Correct answer was 336721 (with my data)
    solution2 = part2(data)  # Correct answer was 91638945 (with my data)

    return solution1, solution2


if __name__ == "__main__":
    for path in sys.argv[1:]:
        print(f"{path}:")
        puzzle_input = pathlib.Path(path).read_text().strip()
        solutions = solve(puzzle_input)
        print('\n'.join(str(solution) for solution in solutions))