Queues and Its Applications : MCQs & PYQs with Explanation

Option C

In a normal or linear queue implemented using an array of size N, the queue becomes full when the value of REAR reaches the last index of the array, that is N−1.

Option C

These operations are performed on a double-ended queue (deque) or a list that allows insertion and deletion at both front and rear.

• InsertFront(x) places x at the beginning.
• InsertRear(x) places x at the end.
• DeleteFront() removes the first element.
• DeleteRear() removes the last element.

Now apply the operations one by one and show the list after each step:

• InsertFront(10) : 10
• InsertFront(20) : 20 10
• InsertRear(30) : 20 10 30
• DeleteFront() : Removes 20 : 10 30
• InsertRear(40) : 10 30 40
• InsertRear(10) : 10 30 40 10
• DeleteRear() : Removes Last 10 : 10 30 40
• InsertRear(15) : 10 30 40 15
• Display() : Prints 10 30 40 15

So, the final list is 10 30 40 15.

Option C

A Circular Queue is a linear data structure in which the last position is connected back to the first position. This allows better memory utilization compared to a simple queue.
Overflow condition occurs when no more elements can be inserted into the circular queue. For a circular queue of size N, overflow occurs in two situations:
When FRONT = 1 and REAR = N

• This means the queue is completely filled from beginning to end.

When FRONT = REAR + 1

• This means the rear position is just behind the front position in circular form, indicating the queue is full.

Option A

In a circular queue implemented using an array, the queue is considered empty when there are no elements stored in it. The most common and standard way to represent an empty circular queue is if front=rear=-1.
When the circular queue is first created, it contains no elements. To show this, both front and rear are initialized to -1. As soon as we insert the first element both front and rear becomes 0. When all elements are deleted again, we reset them to -1 to show the queue is empty.

• When front=rear=0, means one element is present.
• When front=rear+1, this is the condition for circular queue full (no empty space available).

Option B

First, consider the stack operations (LIFO). The stack is initially empty. After push(54) and push(52), the stack becomes [54, 52]. The pop() operation removes 52. Then push(55) and push(62) make the stack [54, 55, 62]. Finally, s=pop() removes the top element 62, so s=62.
Next, consider the queue operations (FIFO). The queue is initially empty. After enqueue(21) and enqueue(24), the queue becomes [21, 24]. The dequeue() operation removes 21. Then enqueue(28) and enqueue(32) make the queue [24, 28, 32]. Finally, q = dequeue() removes 24, so q=24.
Therefore, s+q = 62+24 = 86

Option A

A queue follows the FIFO (First In First Out) principle, whereas a stack follows the LIFO (Last In First Out) principle. 
To implement a queue using stacks, we need two stacks. One stack is used for enqueue operations, and the other stack is used for dequeue operations. 
By transferring elements between the two stacks, the order of elements is reversed, which helps achieve FIFO behavior.

Option B

First, the elements A, B, C, D, E are pushed onto the stack in this order. Since a stack follows LIFO, after all pushes the stack (Top → Bottom) becomes: E, D, C, B, A.

Now, four elements are popped from the stack and inserted into a queue.

Next, two elements are deleted from the queue and pushed back on the stack.

Finally, one item is popped from the stack, which removes the top element D.

Option B

A data structure in which elements are inserted at the rear and deleted from the front follows the FIFO (First In, First Out) principle. This is exactly how a queue works. In a queue, new data always enters from the rear (back or end), and the oldest data is removed from the front.

Option C

A Dequeue stands for Double Ended Queue. It is a linear data structure where:

• Insertions and deletions can occur at both ends (front and rear).
• No insertion or deletion is allowed in the middle.

In priority queue, elements are inserted in any order but removed based on priority, not position.
The threaded binary tree is type of binary tree optimized for in-order traversal, not a linear list.
The linked list allows insertions and deletions at any position, including the middle.

Option C

In a normal Queue, we can insert elements until queue becomes full. But once queue becomes full, we cannot insert the next element even if there is a space in front of queue.
A Circular Queue is a type of queue in which the last position is connected back to the first position, forming a circle. This allows efficient use of memory by reusing empty spaces when elements are deleted. 
Another common name for a circular queue is a Ring Buffer, because conceptually the storage forms a ring where the front and rear wrap around.
If we want to insert new element in circular queue using REAR end, then the value of REAR can be calculated as: REAR=(REAR+1)%CAPACITY
Similarly, when we want to delete existing element from the circular queue using FRONT end, then the value of FRONT can be calculated as: FRONT=(FRONT+1)%CAPACITY

Option B

To reverse a queue from configuration [a, b, c, d] to [d, c, b, a] using only queue operations, the minimum required is 3 deletions and 3 additions.

Option B

A Deque (Double-Ended Queue) is a data structure in which elements can be inserted and deleted at both ends, the front as well as the rear but not in the middle.

• In queue, insertion at rear and deletion at front only.
• In stack, insertion, and deletion at the one end called top of the stack.
• In priority queue, deletion is based on priority, not on ends.

Option B

A queue is a linear data structure in which insertion of elements is performed at one end called rear end and deletion of elements is performed from the other end called front end. This behavior follows the FIFO (First In, First Out) principle.

Option A

A queue is a linear data structure that manages elements in a specific order, like people waiting in line at a ticket counter, the first to arrive is served first. A queue follows the FIFO (First In, First Out) principle.

• LIFO describes a stack.
• LILO is not a standard term for data-structure behavior. Although it would mean the same as FIFO if interpreted literally, but it is not used.

Option C

A Circular Queue is also commonly known as a Ring Buffer. It is a data structure that connects the last position back to the first, forming a circle, which allows efficient reuse of buffer space.

Same as queue the circular queue data structure follows the FIFO (First In, First Out) principle and is widely used in scenarios where fixed size buffer management is needed.
The circular queue is empty (underflow) when front == -1 and full (overflow) when (rear + 1) % capacity == front.