使用递归分解数量

Question

给定数组

bills = [500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01]。

要求编写一个函数decompose()，该功能将分解数组中包含的账单中的金额。

---

例如，decompose(423)将返回包含以下元素的列表

[200, 200, 20, 1, 1, 1]

这是我的代码：

bills = [500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01]
def decompose(amount, lst = []):
    if len(bills) == 1:
        return lst
    if amount > bills[0]:
        lst += [bills[0]]
        amount = amount - bills[0]
        return decompose(bills, lst + [bills[0]])
    return decompose(bills[1:], lst + [bills[0]]) 
print(decompose(523)) 

我的输出是：

Traceback (most recent call last):
  File "test.py", line 94, in <module>
    print(decompose(523)) 
  File "test.py", line 91, in decompose
    return decompose(bills, lst + [bills[0]])
  File "test.py", line 88, in decompose
    if amount > bills[0]:
TypeError: '>' not supported between instances of 'list' and 'int'

我如何分解我的金额？

Answer 1

当最高账单适合该金额时，您应递归从金额中扣除账单价值，或者递归转移到下一个账单上，同时保留相同的金额：

def decompose(amount, bills):
    if not bills:
        return []
    if amount >= bills[0]:
        return [bills[0]] + decompose(amount - bills[0], bills)
    else:
        return decompose(amount, bills[1:])

这样：

bills = [500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01]
decompose(423, bills)

返回：

[200, 200, 20, 2, 1]

Answer 2

您正在尝试提供bills代替当前amount-因此，您会得到错误，因为您无法为list和int进行amount >= bills[0]。

您的代码中还有其他几个错误：

def decompose(amount, bills, lst = None):  # fix here - supply the possible bills as well
    lst = lst or []
    if amount == 0:                      # fix - when amount == 0 you are done
        return lst
    if amount >= bills[0]:      # fix - as long as bills[0] can be deducted, do so (>=)
        lst += [bills[0]]       # bill[0] is already addded no need to do below again
        amount = amount - bills[0]
        return decompose(amount, bills, lst ) # fix - supply same bills, 
    return decompose(amount, bills[1:], lst ) # fix - bill[0] too big, supply bills[1:]
bills = [500, 200, 100, 50, 20, 10, 5, 2, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01]
print(decompose(523, bills)) 

输出：

[500, 20, 2, 1]

您可能需要研究调试：https：//wiki.python.org/moin/pythondebuggingtools逐步浏览您的代码非常有帮助 - 一段时间后，您为这样的小型代码件开发了内部调试器；p>