Catalan number and stack order number, Java programming simulation

Problem Description:

There are 7 integers in the queue from 1 to 7 (from small to large), what is the number of all permutations of the stack after an integer stack?
If the capacity of the integer stack is 4 (the stack can hold up to 4 integers), what is the number of permutations of the stack?

Analysis: For each number I, before it goes into the stack there are i-1 numbers through the stack to the output queue out (do not consider the I-1 numbers in and out of the stack order, because they can be abstracted into F (i-1)), after which there are n-i numbers into the stack and then out of the stack (also do not need to consider their entry and exit ), so that you get the integer i for each last stack, which has an F (i-1) *f (n-i) of the stack order, and the sum is N number order through the stack order.

 Public classCatalan { Public Static intAnswers = 0; //Please implement the Go function     Public Static voidGo (Deque from, Deque to, Stack s) {if(from.size () = = 0 &&S.empty ()) {Answers++; }        Else{Stack S1=S.clone (); Stack S2=S.clone (); //Deque from1 = From.clone (); //Deque from2 = From.clone ();            if(From.size ()! = 0) {S1.push (From.getfirst ());                From.removefirst ();                Go (from, to, S1);            From.addfirst (S1.pop ()); }            if(!S2.empty ())                {To.addlast (S2.pop ());            Go (from, to, S2); }        }    }     Public Static voidMain (string[] args) {Deque from=NewDeque (); Deque to=NewDeque (); Stack s=NewStack ();  for(inti=1;i<=7;i++) {from.addlast (i);        } go (from, to, s);    System.out.println (answers); }}

Catalan number and stack order number, Java programming simulation