Optimisation fibo et ackerman

salut

j'ai deux mini-programme

ici: ackermann

import java.util.Date;

public class ackermann {
public static void main(String[] args) {
long startTime;
long stopTime;
long elapsedTime;
startTime = (new Date()).getTime();
int num = Integer.parseInt(args[0]);
System.out.println("Ack(3," + num + "): " + Ack(3, num));
stopTime = (new Date()).getTime();
elapsedTime = stopTime - startTime;
System.out.println("elapsed time: " + elapsedTime);
}
public static int Ack(int m, int n) {
return (m == 0) ? (n + 1) : ((n == 0) ? Ack(m-1, 1) :
Ack(m-1, Ack(m, n - 1)));
}
}


ici c'est fibo

import java.util.Date;
public class fibo {
public static void main(String args[]) {
long startTime;
long stopTime;
long elapsedTime;
startTime = (new Date()).getTime();
int N = Integer.parseInt(args[0]);
System.out.println(fib(N));
stopTime = (new Date()).getTime();
elapsedTime = stopTime - startTime;
System.out.println("elapsed time: " + elapsedTime);
}
public static int fib(int n) {
if (n < 2) return(1);
return( fib(n-2) + fib(n-1) );
}
}

quelqu'un saurait comment optimiser d'avantage ces deux code?

merci