// MyMath.java
// static methods demonstrating recursion
// To run: MyMath.fib(4) in the Interactions pane

public class MyMath {
  
    // Returns n!
    // Assumes that n is non-negative
    public static int factorial(int n) {
        if (n == 0) {  // base case
            return 1;
        } else {         // recursive case
            return n * factorial(n-1);
        }
    }
  
    // Returns the n-th Fibonacci number
    // Assumes that n is non-negative
    public static int fib(int n) {
        if (n == 0) {        // base case 1
            return 0;
        } else if (n == 1) { // base case 2
            return 1;
        } else {             // recursive case
            return fib(n-1) + fib(n-2);
        }
    }

    // Returns the n-th Fibonacci number
    // Much more efficient version that keeps
    // track of the previous two numbers
    public static int fib2(int n) {
        if (n == 0)
            return 0;
        int prevfib = 0;
        int fib = 1;
        for (int i = 2; i <= n; i++) {
            int newfib = fib + prevfib;
            prevfib = fib;
            fib = newfib;
        }
        return fib;
    }

    // Challenge: implement a recursive version
    // of the efficient algorithm!
}