CODEWITHSUNDEEP
javarecursion
David Meredith
David Meredith

Reputation: 64

Recursive method for loan calculation

I'm trying to write a recursive method that takes 3 parameters (a loan amount, an interest rate, and a monthly payment). The interest is compounded monthly. The goal is to find out how many months it will take to pay off the loan completely. Here is the code I have so far:

    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));
        }

    }

Examples of EXPECTED returns include:

loanLength(1000, 0.10, 200) is paid off in 6 months

loanLength(0, 0.90, 50) is 0 months

But my returns look like:

loanLength(1000, 0.10, 200): 7 months

loanLength(0, 0.90, 50): 0 months

My second test works fine, but my first one is just 1 integer above what it should be. I cannot figure out why. Any help is appreciated.

Upvotes: 0

Views: 2378

Answers (1)

OneCricketeer
OneCricketeer

Reputation: 191844

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)
}

Please note that interest APR is expressed as is, i.e. a $10,000 loan at 10% APR and $500 monthly payments is calculated as 

loanLength(10000, 10.0, 500);

If 0.10 = 10% APR, then change this line

double monthlyInterest = interestAPR / 12;

Upvotes: 3

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