Introduction to queue, its operations explained

2. A queue is open at both its ends. One end is always used to
insert data (enqueue) and the other is used to remove data
(dequeue).
 Queue follows First In First Out (FIFO) methodology, i.e., the
data item stored first will be accessed first.
It has two pointers – front and rear. Front is used for deletion
and rear is used for insertion.
The difference between stack and queue is in removing the
elements. In a stack we remove the item that has been recently
added but in a queue, we remove the item that has been added
at the first.

3. EXAMPLES OF QUEUE

4. OPERATIONS OF QUEUE
Insertion/Enqueue ( ) − Storing an element on the queue.
Deletion/Dequeue ( ) − Removing an element from the queue.
We also need to check the status of the queue
to use it efficiently :
Overflow – To check if queue is full.
Underflow – To check if queue is empty.

6. ALGORITHM OF INSERTION OPERATION
Step 1 − Start
Step 2 – Check if the queue is full.
Step 3 − If the queue is full, display Overflow.
Step 4 − If the queue is not full, increment rear pointer to point to the
next empty space.
Step 5 − Add data element to the queue location, where the rear is
pointing.
Step 6 − End

7. IMPLEMENTATION OF INSERTION OPERATION
0 1 2 3
0 1 2 3
0 1 2 3
0 1 2 3 0 1 2 3
rea
r
rea
r
rea
r
rea
r
rear= -
1

8. CODE FOR INSERTION OPERATION
void insert(int data)
{
if (rear < arr.length - 1)
{
arr[++rear] = data;
System.out.println("Element " + data +" is inserted to
Queue !");
}
else
System.out.println("Overflow !");
}

9. Step 1 − Start
Step 2 – Check if the queue is empty.
Step 3 − If the queue is empty, display Underflow.
Step 4 − If the queue is not empty, access the data where front
is pointing.
Step 5 − Increment front pointer to point to the next available
data element.
Step 6 − End
ALGORITHM OF DELETION OPERATION

10. 0 1 2 3
front=
0
rear=3
IMPLEMENTATION OF DELETION OPERATION
0 1 2 3
0 1 2 3
0 1 2 3 0 1 2 3
fro
nt
fro
nt
fro
nt
front=
4

11. CODE FOR DELETION OPERATION
void delete()
{
if (rear >= front)
System.out.println("Deleted element=" +arr[front++]);
else
System.out.println("Underflow !");
}