DSA/algorithms/Java/queues/circular-queue-linked-list.java

// Java program for insertion and
// deletion in Circular Queue
import java.util.*;
  
class Solution {
  
    // Structure of a Node
    static class Node {
        int data;
        Node link;
    }
  
    static class Queue {
        Node front, rear;
    }
  
    // Function to create Circular queue
    static void enQueue(Queue q, int value)
    {
        Node temp = new Node();
        temp.data = value;
        if (q.front == null)
            q.front = temp;
        else
            q.rear.link = temp;
  
        q.rear = temp;
        q.rear.link = q.front;
    }
  
    // Function to delete element from Circular Queue
    static int deQueue(Queue q)
    {
        if (q.front == null) {
            System.out.printf("Queue is empty");
            return Integer.MIN_VALUE;
        }
  
        // If this is the last node to be deleted
        int value; // Value to be dequeued
        if (q.front == q.rear) {
            value = q.front.data;
            q.front = null;
            q.rear = null;
        }
        else // There are more than one nodes
        {
            Node temp = q.front;
            value = temp.data;
            q.front = q.front.link;
            q.rear.link = q.front;
        }
  
        return value;
    }
  
    // Function displaying the elements of Circular Queue
    static void displayQueue(Queue q)
    {
        Node temp = q.front;
        System.out.printf("\nElements in Circular Queue are: ");
        while (temp.link != q.front) {
            System.out.printf("%d ", temp.data);
            temp = temp.link;
        }
        System.out.printf("%d", temp.data);
    }
  
    /* Driver of the program */
    public static void main(String args[])
    {
        // Create a queue and initialize front and rear
        Queue q = new Queue();
        q.front = q.rear = null;
  
        // Inserting elements in Circular Queue
        enQueue(q, 14);
        enQueue(q, 22);
        enQueue(q, 6);
  
        // Display elements present in Circular Queue
        displayQueue(q);
  
        // Deleting elements from Circular Queue
        System.out.printf("\nDeleted value = %d", deQueue(q));
        System.out.printf("\nDeleted value = %d", deQueue(q));
  
        // Remaining elements in Circular Queue
        displayQueue(q);
  
        enQueue(q, 9);
        enQueue(q, 20);
        displayQueue(q);
    }
}