java - 贷款计算的递归方法

Question

我正在尝试编写一个带有 3 个参数(贷款金额、利率和每月付款)的递归方法。利息按月复利。目标是找出完全还清贷款需要多少个月。这是我到目前为止的代码:

    public static double loanLength(double loan, double interest, double payment) {
    if (payment > loan + loan * interest) {
        return 0;
    } else {
        double completeLoan = loan + (loan * interest);
        double stillOwe = completeLoan - payment;
        if (stillOwe <= 0) {
            return 1;
        } else {
            return 1 + (loanLength(stillOwe, interest, payment));
        }

    }

预期返回的示例包括:

loanLength(1000, 0.10, 200) 在 6 个月内还清

loanLength(0, 0.90, 50) 为 0 个月

但我的返回看起来像:

贷款长度(1000, 0.10, 200):7个月

loanLength(0, 0.90, 50):0 个月

我的第二个测试工作正常，但我的第一个测试仅比应有的值高 1 个整数。我不明白为什么。如有任何帮助，我们将不胜感激。

Answer 1

public static int loanLength(double loan, double interestAPR, double payment) {
    if (loan <= 0) {
        return 0;
    }
    double monthlyInterest = interestAPR / (12 * 100);
    double compounded = loan * (1 + monthlyInterest);
    return 1 + loanLength(compounded - payment, interestAPR, payment);
}

public static void main(String[] args) {
    System.out.println(loanLength(0, 0.90, 50)); // 0
    System.out.println(loanLength(1000, 10.0, 200)); // 6
    System.out.println(loanLength(1000, 0.1, 200)); // 6 (FWIW)
}

请注意，利息年利率按原样表示，即年利率 10% 的 10,000 美元贷款和每月 500 美元的付款计算如下

loanLength(10000, 10.0, 500);

如果 0.10 = 10% APR，则更改此行

double monthlyInterest = interestAPR / 12;