Question

Delete an item from a circular queue and return the index of the next item. (in Java)

Answer 1

The code below will insert, delete, and display the queue:

In queue, the inseretion only take place at end of queue and deletion only take place from the bigning. When deleting an elemnt from queue, the index of queue elements will be updated. So the index of next item after deletion of an item will become 1 in every situation.

import java.util.ArrayList; 

public class CircQ{ 

//class variable declaration
private int size, front, rear; 

//array list declaration of type integer 
private ArrayList<Integer> q = new ArrayList<Integer>(); 

//constructor of circular queue 
CircQ(int size) 
{ 
        this.size = size; 
        this.front = this.rear = -1; 
} 

//insertion function in queue 
public void inQueue(int data) 
{ 
        
        //checking queue is full  
        if((front == 0 && rear == size - 1) || 
        (rear == (front - 1) % (size - 1))) 
        { 
                System.out.print("Queue Full"); 
        } 

        //checking queue empty 
        else if(front == -1) 
        { 
                front = 0; 
                rear = 0; 
                q.add(rear, data); 
        } 

        else if(rear == size - 1 && front != 0) 
        { 
                rear = 0; 
                q.set(rear, data); 
        } 

        else
        { 
                rear = (rear + 1); 
        
                //add new element 
                if(front <= rear) 
                { 
                        q.add(rear, data); 
                } 
        
                //updating old value in else case 
                else
                { 
                        q.set(rear, data); 
                } 
        } 
} 

//deletion function in queue and printing next index
public int deQueue() 
{ 
        int temp; 

        //check queue is empty
        if(front == -1) 
        { 
                System.out.print("Queue Empty"); 
                return -1; 
        } 

        temp = q.get(front);
        //if queue has only one element 
        if(front == rear) 
        { 
                front = -1; 
                rear = -1; 
        } 

        else if(front == size - 1) 
        { 
                front = 0; 
        } 
        else
        { 
                front = front + 1;  //index updation
                
                        System.out.println("Next Index after updation of queue index: " + front);  //printing next index after index updation
        } 
        return temp; 
} 

//display elements in queue 
public void dispQueue() 
{ 
        
        //check queue is empty 
        if(front == -1) 
        { 
                System.out.print("Queue Empty"); 
                return; 
        } 

        System.out.print("Elements in circular queue: "); 

        if(rear >= front) 
        { 
        
                for(int i = front; i <= rear; i++) 
                { 
                        System.out.print(q.get(i)); 
                        System.out.print(" "); 
                } 
                System.out.println(); 
        } 

        else
        { 
                
                //printing elements from front to max_size
                for(int i = front; i < size; i++) 
                { 
                        System.out.print(q.get(i)); 
                        System.out.print(" "); 
                } 

                //printing elements from 0th index till rear
                for(int i = 0; i <= rear; i++) 
                { 
                        System.out.print(q.get(i)); 
                        System.out.print(" "); 
                } 
                System.out.println(); 
        } 
} 

// main function 
public static void main(String[] args) 
{ 
        
        //initialising new object of queue
        CircQ q = new CircQ(5); 
    //inserting 14,22,13,-6 to queue    
        q.inQueue(14); 
        q.inQueue(22); 
        q.inQueue(13); 
        q.inQueue(-6); 
        
        //displaying queue
        q.dispQueue(); 

    //deleting queue
        int x = q.deQueue(); 

        //check queue is empty 
        if(x != -1) 
        { 
                System.out.print("Deleted value = "); 
                System.out.println(x); 
        } 

        q.dispQueue(); 
} 
} 

OUTPUT:

here the queue entered is 14 22 13 -6.

deleting will delete the first element(14) from queue. The index of next item(22) will become 1.

And the new queue will be 22 13 -6