Question

IN JAVA: Delete an item from a circular queue and return the index of the next item

Answer 1

The following is the code for above question

public class Main{
  public static void main(String[] args) {

    CircularQueue q = new CircularQueue();
    //Inserting 5 elements into the Circular Queue
    q.enQueue(7);
    q.enQueue(9);
    q.enQueue(3);
    q.enQueue(4);
    q.enQueue(6);
    //Deleting an item from Circular Queue from front
    int[] element=q.deQueue(); //Store Deleted Element and next item index in element
    if (element[0]!=-1) {
        System.out.println("Deleted Element is " + (element[0]));
      System.out.println("Next Element index is " + (element[1]));
    }
    q.display(); //display the elements in the circular Queue for reference
  }
}
class CircularQueue {
  int front,rear,SIZE=5;
  int items[] = new int[SIZE];

  CircularQueue() {
    front = -1;
    rear = -1;
    SIZE=5;
   
  }
  CircularQueue(int SIZE)
  {
      this.front=-1;
      this.rear=-1;
      this.SIZE=SIZE;
  }

  boolean isFull() {
    if (front==0 && rear==SIZE-1) {
      return true;
    }
    if (front==rear + 1) {
      return true;
    }
    return false;
  }

  
  boolean isEmpty() {
    if (front==-1)
      return true;
    else
      return false;
  }

  void display() {
    int i;
    if (isEmpty()) {
      System.out.println("Empty Queue");
    } else {
      System.out.println("Elements in Circular Queue are : ");
      for (i=front;i!=rear;i=(i+1)%SIZE)
        System.out.print(items[i] + " ");
      System.out.println(items[i]);
    }
  }
  
  void enQueue(int element) {
    if (isFull()) {
      System.out.println("Queue is full");
    } else {
      if (front==-1)
        front=0;
      rear=(rear+1)%SIZE;
      items[rear]=element;
      System.out.println("Inserted " + element +" into Circular Queue");
    }
  }

 
  int[] deQueue() {
    int element;
    if (isEmpty()) {
      System.out.println("Queue is empty");
      return new int[] {-1,-1};
    } else {
      element=items[front];
      if (front==rear) {
        front=-1;
        rear=-1;
      } 
      else {
        front=(front+1)%SIZE;
      }
      return new int[] {element,front}; // Here i am returning deleted element and front because when an item is deleted, we set front to front+1, which means the next element.
    }
  }
}

I am also attaching the output for your reference.

Output:

Inserted 7 into Circular Queue
Inserted 9 into Circular Queue
Inserted 3 into Circular Queue
Inserted 4 into Circular Queue
Inserted 6 into Circular Queue
Deleted Element is 7
Next Element index is 1
Elements in Circular Queue are : 
9 3 4 6

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