Question

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

Answer 1

// Java program for insertion and 
// deletion in Circular Queue 

import java.util.ArrayList; 

  

class CircularQueue{ 

  
// Declaring the class variables. 

private int size, front, rear; 

  
// Declaring array list of integer type. 

private ArrayList<Integer> queue = new ArrayList<Integer>(); 

  
// Constructor 

CircularQueue(int size) 
{ 

    this.size = size; 

    this.front = this.rear = -1; 
} 

  
// Method to insert a new element in the queue. 

public void enQueue(int data) 
{ 

      

    // Condition if queue is full. 

    if((front == 0 && rear == size - 1) || 

      (rear == (front - 1) % (size - 1))) 

    { 

        System.out.print("Queue is Full"); 

    } 

  

    // condition for empty queue. 

    else if(front == -1) 

    { 

        front = 0; 

        rear = 0; 

        queue.add(rear, data); 

    } 

  

    else if(rear == size - 1 && front != 0) 

    { 

        rear = 0; 

        queue.set(rear, data); 

    } 

  

    else

    { 

        rear = (rear + 1); 

      

        // Adding a new element if  

        if(front <= rear) 

        { 

            queue.add(rear, data); 

        } 

      

        // Else updating old value 

        else

        { 

            queue.set(rear, data); 

        } 

    } 
} 

  
// Function to dequeue an element 
// form th queue. 

public int deQueue() 
{ 

    int temp; 

  

    // Condition for empty queue. 

    if(front == -1) 

    { 

        System.out.print("Queue is Empty"); 

          

        // Return -1 in case of empty queue 

        return -1;  

    } 

  

    temp = queue.get(front); 

  

    // Condition for only one element 

    if(front == rear) 

    { 

        front = -1; 

        rear = -1; 

    } 

  

    else if(front == size - 1) 

    { 

        front = 0; 

    } 

    else

    { 

        front = front + 1; 

    } 

      

    // Returns the dequeued element 

    return temp; 
} 

  
// Method to display the elements of queue 

public void displayQueue() 
{ 

      

    // Condition for empty queue. 

    if(front == -1) 

    { 

        System.out.print("Queue is Empty"); 

        return; 

    } 

  

    // If rear has not crossed the max size 

    // or queue rear is still greater then 

    // front. 

    System.out.print("Elements in the " + 

                     "circular queue are: "); 

  

    if(rear >= front) 

    { 

      

        // Loop to print elements from 

        // front to rear. 

        for(int i = front; i <= rear; i++) 

        { 

            System.out.print(queue.get(i)); 

            System.out.print(" "); 

        } 

        System.out.println(); 

    } 

  

    // If rear crossed the max index and 

    // indexing has started in loop 

    else

    { 

          

        // Loop for printing elements from 

        // front to max size or last index 

        for(int i = front; i < size; i++) 

        { 

            System.out.print(queue.get(i)); 

            System.out.print(" "); 

        } 

  

        // Loop for printing elements from 

        // 0th index till rear position 

        for(int i = 0; i <= rear; i++) 

        { 

            System.out.print(queue.get(i)); 

            System.out.print(" "); 

        } 

        System.out.println(); 

    } 
} 

  
// Driver code 

public static void main(String[] args) 
{ 

      

    // Initialising new object of 

    // CircularQueue class. 

    CircularQueue q = new CircularQueue(5); 

      

    q.enQueue(14); 

    q.enQueue(22); 

    q.enQueue(13); 

    q.enQueue(-6); 

      

    q.displayQueue(); 

  

    int x = q.deQueue(); 

  

    // Checking for empty queue. 

    if(x != -1) 

    { 

        System.out.print("Deleted value = "); 

        System.out.println(x); 

    } 

  

    x = q.deQueue(); 

  

    // Checking for empty queue. 

    if(x != -1) 

    { 

        System.out.print("Deleted value = "); 

        System.out.println(x); 

    } 

  

    q.displayQueue(); 

      

    q.enQueue(9); 

    q.enQueue(20); 

    q.enQueue(5); 

      

    q.displayQueue(); 

      

    q.enQueue(20); 
} 
}

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