How to set the function to display the correct banknotes? If the entire amount cannot be withdrawn the function ceases to work

Question

def get_money(money):
 
    lst_banknotes = {1000: 0,
                     500: 0,
                     200: 0,
                     100: 0,
                     50: 2,
                     20: 10,
                     10: 10}
    summa = 0
    res = []
    for k, v in sorted(lst_banknotes.items(), key=lambda x: -x[0]):
        while summa + k <= money and lst_banknotes[k] > 0:
            summa += k
            lst_banknotes[k] -= 1
            res.append(k)
 
    return res
 
print(get_money(1600))

Your `while` loop never ends. What *should* happen in case the amount is not available? — not_speshal, Dec 15 '21 at 15:14
What do you want to happen if there is no combination of bank notes that works? — 001, Dec 15 '21 at 15:20
If there is no combination, the function should not work (generate an error). — Дима Федоров, Dec 15 '21 at 15:29

score 1 · Answer 1 · answered Dec 15 '21 at 15:36

1

raise exceptions when there is insufficient money or when you can't return the exact amount:

def get_money(money):
    
    lst_banknotes = {1000: 0, 500: 0, 200: 0, 100: 0, 50: 2, 20: 10, 10: 10}
    available = sum(k*v for k,v in lst_banknotes.items())
    if money > available:
        raise ValueError(f"Total amount available is {available}")
    
    result = list()
    remaining = money
    for k, v in lst_banknotes.items():
        if v == 0:
            continue
        q = remaining//k
        notes = min(q, v)
        
        result += [k]*notes
        remaining -= k*notes
    
    if sum(result) != money:
        raise ValueError("Unable to fetch exact amount.")
    return result

Output:

>>> get_money(350)
[50, 50, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 10, 10, 10, 10, 10]

>>> get_money(205)
ValueError: Unable to fetch exact amount.

>>> get_money(500)
ValueError: Total amount available is 400

answered Dec 15 '21 at 15:36

not_speshal

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What if I have a wordlist in the file admin_balance.json {"10": 1, "20": 2, "50": 0, "100": 2, "200": 1, "500": 0, "1000": 1}? – Дима Федоров Dec 15 '21 at 15:51
Convert them to `int` when you read the json. – not_speshal Dec 15 '21 at 15:53
I did so lst_banknotes = {int(key): value for key, value in data.items()} , but it doesn't work well – Дима Федоров Dec 15 '21 at 16:01
I don't know what "doesn't work well" means. Are you getting errors? Something else? – not_speshal Dec 15 '21 at 16:02
with open(path, 'r') as f: data = json.load(f) lst_banknotes = {int(key): value for key, value in data.items()} available = sum(k * v for k, v in lst_banknotes.items()) – Дима Федоров Dec 15 '21 at 16:06
Says ValueError: Unable to get exact amount – Дима Федоров Dec 15 '21 at 16:07
in case of lst_banknotes = {1000: 0, 500: 0, 200:0, 100: 1, 50: 1, 20:10, 10: 0} ValueError: Unable to get the exact amount. print(get_money(160)) – Дима Федоров Dec 15 '21 at 16:17
I see - this just tries to pick the most notes of each type. So it picks 100, 50 and then doesn't find a 10. If you want to pick 20, 20, 20 and ignore 50, you'll need a much more complicated algorithm where you should compute every possible combination to get 160 and return the one that matches. – not_speshal Dec 15 '21 at 17:28
You would need to implement something like [here](https://stackoverflow.com/questions/34517540/find-all-combinations-of-a-list-of-numbers-with-a-given-sum) – not_speshal Dec 15 '21 at 17:29
Looks very difficult – Дима Федоров Dec 15 '21 at 17:34

How to set the function to display the correct banknotes? If the entire amount cannot be withdrawn the function ceases to work

1 Answers1

Output: