Peek Front Element of Queue in DSA C - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of peeking the front element in this queue?

Consider a queue implemented using an array with front at index 0 and rear at index 3. The queue elements are [10, 20, 30, 40]. What will be the output of the peek operation?

DSA C

int queue[] = {10, 20, 30, 40};
int front = 0;
int rear = 3;
int peek = queue[front];
printf("%d\n", peek);

A 30

B 40

C 10

D 0

💡 Hint

The front element is the first element inserted in the queue.

In a queue, the front points to the first element inserted. Here, front is 0, so queue[front] is 10.

❓ Predict Output

intermediate

What happens when peeking an empty queue?

Given a queue with front = -1 and rear = -1 indicating it is empty, what will happen if we try to peek the front element?

DSA C

int front = -1;
int rear = -1;
if(front == -1) {
    printf("Queue is empty\n");
} else {
    printf("%d\n", queue[front]);
}

A Queue is empty

B 0

C Garbage value

D Segmentation fault

💡 Hint

Check the condition that indicates the queue is empty before peeking.

When front is -1, the queue is empty, so peeking should not access any element and print 'Queue is empty'.

🔧 Debug

advanced

Why does this peek function cause an error?

This peek function is intended to return the front element of a queue. Identify the error and its cause.

DSA C

int peek(int queue[], int front, int rear) {
    if(front > rear) {
        printf("Queue is empty\n");
        return -1;
    }
    return queue[rear];
}

A Incorrect empty queue condition causes runtime error

B Returns rear element instead of front element

C Returns front element correctly

D Syntax error due to missing semicolon

💡 Hint

Peek should return the element at the front index, not rear.

The function returns queue[rear], which is the last element, not the front. It should return queue[front].

🧠 Conceptual

advanced

What is the time complexity of peeking the front element in a queue?

Assuming a queue is implemented using a linked list or array, what is the time complexity of the peek operation?

A O(1)

B O(n)

C O(log n)

D O(n^2)

💡 Hint

Peek just returns the front element without traversal.

Peek accesses the front element directly, so it takes constant time O(1).

🚀 Application

expert

After these operations, what is the front element of the queue?

A queue is initially empty. We perform enqueue(5), enqueue(10), dequeue(), enqueue(15), dequeue(), enqueue(20). What is the front element now?

DSA C

Operations:
1. enqueue(5)
2. enqueue(10)
3. dequeue()
4. enqueue(15)
5. dequeue()
6. enqueue(20)

Assume standard FIFO queue behavior.

A 10

B 5

C 20

D 15

💡 Hint

Track the queue state after each operation carefully.

After enqueue(5) and enqueue(10), queue is [5,10]. dequeue removes 5, queue is [10]. enqueue(15) adds 15, queue is [10,15]. dequeue removes 10, queue is [15]. enqueue(20) adds 20, queue is [15,20]. Front is 15.