Ex_15.java

package Big_O;

public class Ex_15 {
	public static int factorial(int n) {
	    if (n < 0) {
	        return -1;
	    } else if (n == 0) {
	        return 1;
	    } else {
	        return n * factorial(n - 1);
	    }
	}
	
	public static void main(String[] args) {
		System.out.println(factorial(4));
	}	
}