Implementation of Queues using two Stack in Java

January 20, 2021

IMPLEMENTAION OF QUEUES USING TWO STACK

How to implement Queue using two Stack in Java ?

In this page we will discuss how to implement queue using stack in java . In other words we will be making a queue in which operations such as enqueue and dequeue are done based on push and pop operations .

Let us see how to do this thing in detail.

                                                      Basic Operations of Queue

  • Enqueue: When we want to add an element to the end of the queue
  • Dequeue: when we want to Remove an element from the front of the queue
  • IsEmpty: Check if the queue is empty
  • IsFull: Check if the queue is full
  • Peek: Get the value of the front of the queue without removing it

ALGORITHMS:

  • ENQUEUE:
static void addqueue(int a) 
    { 
        // Move all elements from p1 to p2 
        while (!p1.isEmpty()) 
        { 
            p2.push(p1.pop()); 
            
        } 
        p1.push(a); 
 while (!p2.isEmpty()) 
        { 
            p1.push(p2.pop()); 
            
        } 
    } 
  • DEQUEUE:
static int deletequeue() 
    { 
        //  first stack is empty 
        if (p1.isEmpty()) 
        { 
            System.out.println(“empty queue”); 
            
        }  
        int a = p1.peek(); 
        p1.pop(); 
        return a; 
    } 

Java code to implement queue using stacks :

// Java program to implement Queue using stacks
import java.util.*; 

class prepinsta 
{ 
static class Queue 
{ 
    static Stack<Integer> p1 = new Stack<Integer>(); 
    static Stack<Integer> p2 = new Stack<Integer>(); 

    static void addqueue(int a) 
    { 
        // Move all elements from p1 to p2 
        while (!p1.isEmpty()) 
        { 
            p2.push(p1.pop()); 
            
        } 

        
        p1.push(a); 

        
        while (!p2.isEmpty()) 
        { 
            p1.push(p2.pop()); 
            
        } 
    } 

    // Dequeue an item from the queue 
    static int deletequeue() 
    { 
        //  first stack is empty 
        if (p1.isEmpty()) 
        { 
            System.out.println(“empty queue”); 
            
        } 

        // Return top of p1 
        int a = p1.peek(); 
        p1.pop(); 
        return a; 
    } 
}


public static void main(String[] args) 
{ 
    Queue queue = new Queue(); 
    queue.addqueue(2); 
    queue.addqueue(4); 
    queue.addqueue(6); 
    queue.addqueue(8); 


    System.out.println(queue.deletequeue()); 
    System.out.println(queue.deletequeue()); 
    System.out.println(queue.deletequeue()); 
    System.out.println(queue.deletequeue()); 
} 
} 
 



Output:

2

4

6

8