Trace a Queue (called Q) through the following operations: Queue Q = new Queue()

Question

Trace a Queue (called Q) through the following operations:

Queue Q = new Queue();

Q.enqueue(new Integer(4));

Q.enqueue(new Integer(3));

//a) What is the content of the queue at this point?

Integer Y = Q.dequeue();

Q.enqueue(new Integer(7));

Q.enqueue(new Integer(2));

Q.enqueue(new Integer(5));

Q.enqueue(new Integer(9));

//b) What is the content of the queue at this point?

Integer Y = Q.dequeue();

Q.enqueue(new Integer(3));

Q.enqueue(new Integer(9));

//c) What is the content of the queue at this point?

Explanation / Answer

Queues: First In - First Out (FIFO)

·         Enqueue()- store or add item to the queue

·         Dequeue()- remove an item form the queue

In queue, dequeue data, pointed by front pointer and while enqueing data in queue we take help of rear pointer.

Enqueue Operation ():

Step 1 Check if queue is full.

Step 2 If a queue is full, produce overflow error and exit.

Step 3 If a queue is not full, increment rear pointer to point next empty space.

Step 4 Add data element to the queue location, where the rear is pointing.

Step 5 return success.

Initializing an Empty Queue: [null]

Front,rear | |, initially front and rear ill be same.

Enqueue 4 in the queue: | 4 | (head is 4)

Enqueue 3 in the queue: | 3 | 4 | (head is still 4)

Rear front

    | 3 | 4|

Front=4, rear =3

Total elements in queue is 2 (3,4)

Dequeue Operation ()

Step 1 Check if the queue is empty.

Step 2 If the queue is empty, produce underflow error and exit.

Step 3 If the queue is not empty, access data where front is pointing.

Step 4 Increment front pointer to point next available data element.

Step 5 return success.

(b)

| 9 | 5 | 2 | 7 |

Rear =9 and front =7

The total elements in the queue 4 (7, 2, 5, 9)

9à5à2à7 (7 is dequeue from front side of the queue, next 2..)

(c)

| 9 | 3 |

Rear =9 and front=3

Total elements =2 (3, 9)

dequeue takes place from element 3.

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