/* File: FibRec.java - March 2011 */
package l04;

/**
 * Compute and display the Fibonacci number of the input argument
 * using an improved recursive algorithm. Long values are returned
 * so that quite large inputs (e.g. 100) are possible.
 *
 * Sample usage: java l04.FibRec 5
 *
 * @author Michael Albert
 *
 */

public class FibRec{

   public static void main(String[] args) {

      int n = Integer.parseInt(args[0]);
      System.out.println("Fib(" + n + ") = " + fib(n));

   }

   public static long fib(int n) {
      return fibHelper(0, 1, n);
   }

   // In fibHelper, a and b are always a successive pair of Fibonacci
   // numbers, and n represents the number of steps remaining until
   // the answer we want is held in b.
   public static long fibHelper(long a, long b, int n) {
      if (n == 0) return b;
      return fibHelper(b, a+b, n-1);
   }


}