Question

I’m really getting the hang of recursion (or so I think), but this problem is tripping me up. I’m trying to return 1 + 1/2 + 1/3 + … + 1/n, but no matter what I try the method returns 1.0. I cannot for the life of me figure out what’s wrong.

public static double harmonic(int n) {
    if(n == 1) {
        return 1;
    } else {
        return (1 / n) + (1 / harmonic(n - 1));
    }
}

Answer 1

Well, for one, you don’t want to return (1 / n) + (1 / harmonic(n - 1)), but also you need to use double arithmetic:

public static double harmonic(int n) {
    if(n == 1) {
        return 1.0;
    } else {
        return (1.0 / n) + harmonic(n - 1);
    }
}

If you left it as 1 / harmonic you’d return another function entirely:

(1 / n) + 1 / ( 1 / (n – 1) + 1 / ( 1 / (n – 2) + 1 / (…) ) )

That is a very confusing function to figure out, btw, but I think (with my 3rd time editing it) I got it right this time.