/*
Author  : Michael Robinson
Program : recursion.java
Purpose : to implement recursion functions
          in this example we want to find the
          factorial of 7, 
          The mathematical representation is 7! = 5040 
          which means  7 * 6 * 5 * 4 * 3 * 2 * 1
          
          We can find the factorial of any number by passing its
          value to the method factorial( int n ) 

          7! = 7*6! = 7*720 = 5040
          6! = 6*5! = 6*120 =  720
          5! = 5*4! = 5*24  =  120  
          4! = 4*3! = 4*6   =   24 
          3! = 3*2! = 3*2   =    6  
          2! = 2*1! = 2*1   =    2
          1! = 1    = 1     =    1  //base case
          
          note 0! = 1 always
    
          NOTE: JAVA WILL START GIVING WRONG VALUES FOR FACTORIAL RESULTS
                CREATE A VALIDATION SECTION TO DETECT AND STOP AT THAT POINT            


Updated : January 13, 2012
*/


import java.util.Scanner;

class recursion
{
   
    public static void pause()
    {
        System.out.print( "Press any key to continue ...");
        Scanner anykey = new Scanner(System.in);
        String temp  = anykey.nextLine();
    }
   
   
    public static long factorial( int n )
    {
        System.out.printf("Processing factorial( %d )\n",  n);
        pause();
      
        if(n <= 1) //base case
        {
    	    System.out.printf("\nReached base case, returning %d\n\n", n); 
       	    System.out.printf("Now returning the accumulated values from RAM\n");    	 
            return 1; 
        }
        else
        {
            System.out.printf("\nDoing recursion by calling factorial( %d - 1 )\n",  n );
            long counter = n * factorial(n - 1); //doing recursion by calling factorial(n - 1)
         
            System.out.printf("Receiving results of factorial( %d ) =  %d * %d! = %d\n", n, n, (n-1), counter);
            return counter;
        }

    }//end public static long fact(long n)

	
    public static void main(String args[])
    {
        System.out.println( "\nRecursion Program" );	
        System.out.println( "=================" );	
     
        System.out.print( "Enter an integer to do recursion : ");
        Scanner recur = new Scanner(System.in);
        int recursion  = recur.nextInt();
        factorial( recursion );
       
    }
	
}//end class recursion