package hello;

 import java.util.*;

 public class TwoStackOneQueue<E> {

     private Stack<E> s1 = new Stack<>();

     private Stack<E> s2 = new Stack<>();

     public void enqueue(E item){

         s1.push(item);

     }

     public E dequeue(){

         if (s2.empty()){

             if(s1.empty()){

                 throw new ArrayIndexOutOfBoundsException();

             }else{

                 popS1ToS2();

                 return s2.pop();

             }

         }else{

             return s2.pop();

         }

     }

     private void popS1ToS2(){

         while(!s1.empty()){

             s2.push(s1.pop());

         }

     }

     public static void main(String[] args){

         TwoStackOneQueue<Integer> tsoq = new TwoStackOneQueue<>();

         for (int i = 0; i < 20; i++){

             tsoq.enqueue(i);

         }

         for (int i = 0; i < 10; i++) {

             System.out.println(tsoq.dequeue());

         }

         for (int i = 20; i < 40; i++){

             tsoq.enqueue(i);

         }

         for (int i = 0; i < 30; i++) {

             System.out.println(tsoq.dequeue());

         }

     }

 }