Recursive Fibonacci

Question

I\'m having a hard time understanding why

#include 

using namespace std;

int fib(int x) {
    if (x == 1) {
        return 1;
    } else {
         


        

Answer 1

I think that all that solutions are inefficient. They require a lot of recursive calls to get the result.

unsigned fib(unsigned n) {
    if(n == 0) return 0;
    if(n == 1) return 1;
    return fib(n-1) + fib(n-2);
}

This code requires 14 calls to get result for fib(5), 177 for fin(10) and 2.7kk for fib(30).

You should better use this approach or if you want to use recursion try this:

unsigned fib(unsigned n, unsigned prev1 = 0, unsigned prev2 = 1, int depth = 2)     
{
    if(n == 0) return 0;
    if(n == 1) return 1;
    if(depth < n) return fib(n, prev2, prev1+prev2, depth+1);
    return prev1+prev2;
}

This function requires n recursive calls to calculate Fibonacci number for n. You can still use it by calling fib(10) because all other parameters have default values.