package stack_and_queue;

/* Java Program to implement a stack using two queue */

import java.util.*;

import java.util.Queue;

class P20 {

static class StackByQueues {

// Two inbuilt queues

static Queue<Integer> q1 = new LinkedList<>();

static Queue<Integer> q2 = new LinkedList<>();

// To maintain current number of

// elements

static int curr_size;

StackByQueues() {

curr_size = 0;

}

void push(int x) {

curr_size++;

// Push x first in empty q2

q2.add(x);

// Push all the remaining

// elements in q1 to q2.

while (!q1.isEmpty()) {

q2.add(q1.peek());

q1.remove();

}

// swap the names of two queues

Queue<Integer> q = q1;

q1 = q2;

q2 = q;

}

static void pop() {

// if no elements are there in q1

if (q1.isEmpty())

return;

q1.remove();

curr_size--;

}

static int top() {

if (q1.isEmpty())

return -1;

return q1.peek();

}

static int size() {

return curr_size;

}

}

// driver code

public static void main(String[] args) {

StackByQueues s = new StackByQueues();

s.push(1);

s.push(2);

s.push(3);

System.out.println("current size: " + StackByQueues.size());

System.out.println(StackByQueues.top());

StackByQueues.pop();

System.out.println(StackByQueues.top());

StackByQueues.pop();

System.out.println(StackByQueues.top());

System.out.println("current size: " + StackByQueues.size());

}

}