class factorials
{ 
  public static void main(String[] args)
  {
     int a;
     fact A = new fact();
     System.out.println("\nthe factorial of 6 is ");
     a = A.f1(6);
     System.out.println( a );
     System.out.println("with tail-recursion it's also ");
     a = A.f2(6,1);
     System.out.println( a );
     System.out.println("without recursion it's still ");
     a = A.f3(6);
     System.out.println( a );     
  } 
}


class fact
{
   public int f1(int n)
   {
       int a;
       if (n<2) a=1;
         else a = n * (this.f1(n-1));
       return a;
   }

   public int f2(int n, int accum)  // accum must be initially 1
   {
       int a; 
       if (n<2) a = accum;
       else a = this.f2(n-1,accum*n);
       return a;
   }

   public int f3(int n)
   {
       int accum = 1;
       while (1<n)
       {
          accum = accum*n;
          n = n-1;
       }
       return accum;
   }
} // fact