/*

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/**

*

* @author Dell

*/

// we use two stacks , to represent a queue , we select an element from the top of the

// stack2 as oldest elements will be added on top of stack2 , hence it can represent queue datastructure

// QUEUE represents FIFO , thats is oldest element is removed first and stack in the inverse of STACK

//STACK removes most recent elements added to the stack.

import java.util.*;

public class QueueUsingTwoStack {

//declaring two stacks to perform stack operation

static Stack<Integer> st1 = new Stack<Integer>();

static Stack<Integer> st2 = new Stack<Integer>();

public static void enqueue(int e){

st1.push(e);

Iterator<Integer> itr = st1.iterator();

while(itr.hasNext()){

//st1.push(st1.pop());

System.out.print(itr.next() + " ");

}

System.out.println("");

}

public static void dequeue(){

//if stack 2 is not empty , then we pop from it.

if(!st2.isEmpty()){

System.out.println("Popped element is ::" + st2.pop());

}

// if stack 1 is empty that means no more elements added to the queue, hence we display no elements in queue.

else if(st1.isEmpty()){

System.out.println("No element in the queue");

}

//if stack2 is empty and new elements are added in stack1 then we inverse the stack1 by popping from stack1 and pushing it to stack2.

if(st2.isEmpty()){

Iterator<Integer> itr = st1.iterator();

while(itr.hasNext()){

st2.push(st1.pop());

}

Iterator<Integer> itr2 = st2.iterator();

while(itr2.hasNext()){

System.out.print(itr2.next() + " ");

}

System.out.println("");

}

}

public static void main(String[] args){

enqueue(10);

enqueue(20);

enqueue(40);

dequeue();

enqueue(50);

enqueue(60);

enqueue(70);

enqueue(80);

enqueue(90);

enqueue(140);

enqueue(100);

enqueue(200);

enqueue(400);

dequeue();

dequeue();

dequeue();

dequeue();

dequeue();

dequeue();

dequeue();

}

}