ctciCh3Q5

import java.util.Stack;

public class MyQueue {
    private Stack<Integer> oldStack;
    private Stack<Integer> newStack;

    public MyQueue(){
        oldStack = new Stack<Integer>();
        newStack = new Stack<Integer>();
    }

    public void enqueue(int data){
        newStack.push(data);
    }

    public Integer dequeue(){
        /*shift element from newStack to oldStack, while reverse the element order*/
        shift(newStack, oldStack);
        return oldStack.pop();
    }

    public int size(){
        return oldStack.size()+newStack.size();
    }

    private void shift(Stack<Integer> src, Stack<Integer> dest){
        /*only when oldStack is empty do we have to do the shift*/
        if(dest.isEmpty()){
            while(!src.isEmpty()){
                dest.push(src.pop());
            }
        }
    }
}