Question

I need to solve this recurrence function: f(n) = 5*f(n-1) – 2*f(n-2), with f(0)=1 and f(1)=2. I wrote the below code, but it is not giving the correct answer — it outputs 164, for example, when n = 4, although the correct answer is 26 (assuming I did my math correctly).

public static int recurFunction(int n) {
    if(n == 0) {
        return 1;
    } else if(n == 1) {
        return 2;
    } else {
        n = ((5 * recurFunction(n - 1)) - (2 * recurFunction(n - 2)));
        return n;
    }
}

Answer 1

Your math is wrong 🙂

f(n) = 5*f(n-1) – 2*f(n-2)

f(0) = 1
f(1) = 2
f(2) = 5 * f(1) - 2 * f(0) = 5 * 2 - 2 * 1 = 10 - 2 = 8
f(3) = 5 * f(2) - 2 * f(1) = 5 * 8 - 2 * 2 = 40 - 4 = 36
f(4) = 5 * f(3) - 2 * f(2) = 5 * 36 - 2 * 8 = 180 - 16 = 164