Advent of Code 2019 Day 14

day_14.py

import math
from collections import Counter

from funcy import post_processing
from parse import parse
from scipy.optimize import minimize_scalar


@post_processing(dict)
def parse_input(input_str):
    quantity_pattern = '{num:d} {unit:w}'
    for line in input_str.strip().splitlines():
        left_str, right = line.split(' => ')
        lefts = [parse(quantity_pattern, input) for input in left_str.split(', ')]
        lefts = {input['unit']: input['num'] for input in lefts}
        right = parse(quantity_pattern, right)
        yield right['unit'], {'right_num': right['num'], 'lefts': lefts}


def calc_ore(eqs, fuel):
    chemicals = Counter()
    chemicals['FUEL'] = fuel

    last_chemicals = None

    while last_chemicals != chemicals:
        last_chemicals = chemicals.copy()

        for right, eq_data in eqs.items():
            for got_unit, got_num in list(chemicals.items()):

                if got_unit == right and got_num > 0:
                    mult = math.ceil(got_num / eq_data['right_num'])
                    chemicals[got_unit] -= mult * eq_data['right_num']

                    for left_unit, left_num in eq_data['lefts'].items():
                        chemicals[left_unit] += mult * left_num

    return chemicals['ORE']


def part_one(input_str):
    eqs = parse_input(input_str)
    return calc_ore(eqs, fuel=1)


def part_two(input_str):
    eqs = parse_input(input_str)
    max_ore = 1e12

    def fuel_error(fuel_quota):
        ore = calc_ore(eqs, int(fuel_quota))
        print(fuel_quota, ore)

        ore_left = max_ore - ore
        if ore_left < 0:
            # Penalise using more than the quota
            return abs(ore_left) * 100
        return ore_left

    ore_per_fuel = calc_ore(eqs, fuel=1)
    fuel_estimate = max_ore / ore_per_fuel

    fuel = minimize_scalar(
        fuel_error,
        bracket=(fuel_estimate, 2 * fuel_estimate)
    ).x
    return int(fuel)

Yes, once you have a complex enough problem, being able to black box it like this is a huge plus.