Fibonacci Sequence in Java taking too long?

Question

I\'m trying to find the sum of the Fibonacci sequence in Java, but the run time is taking way too long (or is it suppose to?). This slows down anytime I use an integer past

Answer 1

Recursive solutions don't necessarily have to be slow. If you were to use this tail-recursive solution, you'd save up a lot of memory and still achieve great speed (e.g. Fib(10000) runs in 1.1s on my machine).

Here n is the sequence number for which you're calculating Fibonacci number, while f0 and f1 are two accumulators, for previous and current Fibonacci numbers respectively.

public class FibonacciRec {
    public static int fib(int n, int f0, int f1) {
        if (n == 0) {
            return f0;
        } else if (n == 1){
            return f1;
        } else {
            return fib(n-1, f1, f0+f1);
        }
    }

    public static void main(String[] args) {
        System.out.println(fib(10, 0, 1));
    }
}