python - 信用计算器产生错误的输出

我需要计算所需的最低每月固定付款额，以便在12个月内还清信用卡余额。正确的答案应该是310，但我得到340。我正在编辑代码几个小时，但没有找到合适的解决方案。怎么了如何解决？

balance = 3329
annualInterestRate = 0.2
payment = 10

def year_balance(init_payment, init_balance):
    """ Calculates total debt after 12 months """
    interest_sum = 0
    for month in range(12):
        # balance after monthly payment
        unpaid = init_balance - init_payment
        # monthly interest of remaining balance
        interest = unpaid * (annualInterestRate / 12.0)
        interest_sum += interest
    yearly = init_balance + interest_sum # total debt after 12 months
    return yearly

total = year_balance(payment, balance) # total debt after 12 months

while total - payment * 12 > 0:
# checks if payment is big enough to fully repay the credit after 12 months
    payment += 10

print "Lowest payment: ", payment

最佳答案

我们需要为每个新的付款金额运行余额计数功能，因为对于大笔付款，利息金额会较小。所以

balance = 3329
annualInterestRate = 0.2
payment = 10


def year_balance(init_payment, init_balance):
    """ Calculates total debt after 12 months """
    interest_sum = 0
    unpaid = init_balance
    for month in range(12):
        # balance after monthly payment
        unpaid -= init_payment
        # monthly interest of remaining balance
        unpaid += unpaid * (annualInterestRate / 12.0)
    return unpaid

while year_balance(payment, balance) > 0:
    payment += 10

print("Lowest payment: ", payment)

注意：这种情况是为了防止您在信用期开始之前付款。如果一个月后完成了此操作，则应首先添加每月利率。