fibonacci series - recursive summation

Question

Ok, I initially wrote a simple code to return the Fibonacci number from the series based on the user input..

n=5 will produce 3..

static int fibonacci(in         


        

Answer 1

Recursively is a very inefficient way to calculate the Fibonacci number.After the number 43 it will take more then 30 sec till you'll have the answer. I tried to find out how much time will take to calculate the number 52 and it took about 47 minutes. So the time grows very fast.

The recursive code:

private int calculateRecursivelyInt(int fnum)
    {
        if (fnum == 0)
            return 0;
        if (fnum == 1)
            return 1;

        return calculateRecursivelyInt(fnum - 1) + calculateRecursivelyInt(fnum - 2);
    }

Loops are much more efficient

    //This method will be able to calculate till the F46 because int can't hold a 
    // bigger number. You can calculate till 92 with a type long and till 93 with
    // unsigned long in C#.

    private int calculateLoopInt(int num)
    {
        int fnum = 0;
        int val1 = 0;
        int val2 = 1;

        for (int i = 0; i < num; i++)
        {
            if (num == 1)
                fnum = 1;
            else if (i > 0)
            {
                fnum = val1 + val2;
                val1 = val2;
                val2 = fnum;
            }
        }
        return fnum;
    }