Recursive Fibonacci memoization

Question

I need some help with a program I\'m writing for my Programming II class at universtiy. The question asks that one calculates the Fibonacci sequence using recursion. One mus

Answer 1

public class FiboSeries {

    // first two terms of Fibonacci
    int x1 = 0;
    int x2 = 1;
    long xn; // nth number in Fibo series
    long[] array; // an array for implementing memoization

    // print the Nth number of Fibonacci - logic is f(n) = f(n-1) + f(n-2)

    long fibo(int n) {

        // initialize the array having n elements if it does not exist already
        if (array == null) {

            array = new long[n + 1];

        }

        // Fetch the memoized value from the array instead of recursion
        // for instance, fibo(3) will be calculated just once and stored inside this
        // array for next call
        if (array[n] != 0)

        {
            xn = array[n];
            return xn;
        }

        // value of fibo(1)
        if (n == 1) {
            xn = x1;

        }

        // value of fibo(2)
        if (n == 2) {
            xn = x2;

        }

        // value of Fibo(n) using non linear recursion
        if (n > 2) {

            xn = fibo(n - 1) + fibo(n - 2);
        }

        // before returning the value - store it at nth position of an array
        // However, before saving the value into array, check if the position is already 
        //full or not

        if (array[n] == 0) {

            array[n] = xn;
        }

        return xn;

    }

    public static void main(String[] args) {

        FiboSeries f = new FiboSeries();

        int n = 50;
        long number = f.fibo(n);

        System.out.println(number);

    }


}