aoc_14b.py

fin = open('input_14.txt')
rx = {}
# rx = {'FUEL':[1, [(3,'ABC'), (5,'DEF'), ...]]}
# rx[substance][0] = amount substance produced
# rx[substance][1] = list of (# required, reactant) pairs

for line in fin:  # set up the reaction scheme
    educts, product = line.strip().split('=>')
    p_amount, p_name = product.split()[0], product.split()[1]
    rx[p_name] = [int(p_amount), []]
    for educt in educts.split(','):
        e_amount, e_name = educt.split()[0], educt.split()[1]
        rx[p_name][1].append((int(e_amount), e_name))

# print(rx)


def ore_for(substance, req_amount):
    store = {}

    def _ore_for(substance, req_amount):
        if substance == 'ORE':
            return req_amount
        if substance not in store:
            store[substance] = 0

        to_produce = req_amount - store[substance]
        cycles = (to_produce - 1) // rx[substance][0] + 1
        store[substance] = cycles * rx[substance][0] - to_produce
        ore = 0
        for e_amount, educt in rx[substance][1]:
            # print(runfactor, '*', e_amount, 'of', educt)
            ore += _ore_for(educt, cycles * e_amount)
        return ore
    return _ore_for(substance, req_amount)


def fuel_from(orestore):
    request_lower = orestore // ore_for('FUEL', 1)
    request_higher = 2 * request_lower

    itercount = 0

    while True:
        if request_higher - request_lower <= 1:
            print(itercount, "iterations")
            return request_lower
        request = (request_higher + request_lower) // 2
        ofr = ore_for('FUEL', request)  # ore for request
        if ofr > orestore:
            request_higher = request
        if ofr <= orestore:
            request_lower = request
        itercount += 1


fuelmax = fuel_from(10**12)
print(fuelmax, ore_for('FUEL', fuelmax))