Peek Front Element of Queue in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to peek the front element of the queue.

DSA C#

Queue<int> queue = new Queue<int>();
queue.Enqueue(10);
queue.Enqueue(20);
int front = queue.[1]();
Console.WriteLine(front);

Drag options to blanks, or click blank then click option'

APop

BPeek

CFront

DTop

Attempts:

3 left

💡 Hint

Common Mistakes

Using Pop() which is not a method of Queue in C#.

Using Front or Top which are not valid Queue methods.

The Peek() method returns the front element of the queue without removing it.

2fill in blank

medium

Complete the code to check if the queue is not empty before peeking.

DSA C#

Queue<string> queue = new Queue<string>();
queue.Enqueue("apple");
if (queue.[1] > 0) {
    string front = queue.Peek();
    Console.WriteLine(front);
}

Drag options to blanks, or click blank then click option'

ACapacity

BLength

CCount

DSize

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length which is not a property of Queue.

Using Size or Capacity which are not correct for this check.

The Count property gives the number of elements in the queue.

3fill in blank

hard

Fix the error in the code to correctly peek the front element of the queue.

DSA C#

Queue<double> queue = new Queue<double>();
queue.Enqueue(3.14);
double front = queue.[1]();
Console.WriteLine(front);

Drag options to blanks, or click blank then click option'

APeek()

BFront

CFront()

DPeek

Attempts:

3 left

💡 Hint

Common Mistakes

Using Peek without parentheses.

Using Front which is not a Queue method.

Peek is a method and must be called with parentheses: Peek()

4fill in blank

hard

Fill both blanks to safely peek the front element only if the queue is not empty.

DSA C#

Queue<char> queue = new Queue<char>();
queue.Enqueue('A');
if (queue.[1] > 0) {
    char front = queue.[2]();
    Console.WriteLine(front);
}

Drag options to blanks, or click blank then click option'

ACount

BLength

CPeek

DPop

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length instead of Count.

Using Pop() which removes the element.

Use Count to check if queue has elements and Peek() to get the front element.

5fill in blank

hard

Fill all three blanks to create a queue, add elements, and peek the front element safely.

DSA C#

Queue<string> queue = new Queue<string>();
queue.[1]("first");
queue.[2]("second");
if (queue.[3] > 0) {
    Console.WriteLine(queue.Peek());
}

Drag options to blanks, or click blank then click option'

AEnqueue

BAdd

CCount

DPush

Attempts:

3 left

💡 Hint

Common Mistakes

Using Add or Push which are not Queue methods in C#.

Using Length instead of Count.

Use Enqueue to add elements and Count to check if queue is not empty before peeking.

Practice

1. What does the Peek() method do in a queue?

easy

A. Checks if the queue is empty

B. Returns the front element without removing it

C. Adds an element to the back of the queue

D. Removes and returns the front element

Solution

1. Step 1: Understand the purpose of Peek()

   The Peek() method is designed to look at the front element of the queue without changing the queue itself.

2. Step 2: Differentiate from other queue methods

   Unlike Dequeue() which removes the front element, Peek() only returns it without removal.

3. Final Answer:

   Returns the front element without removing it -> Option B

4. Quick Check:

   Peek() returns front element without removal [OK]

Hint: Peek shows front without removing it [OK]

Common Mistakes:

• Confusing Peek() with Dequeue()
• Thinking Peek() removes the element
• Assuming Peek() adds elements

2. Which of the following is the correct syntax to peek the front element of a queue named myQueue in C#?

easy

A. myQueue.Front();

B. myQueue.GetFront();

C. myQueue.Peek();

D. myQueue.Top();

Solution

1. Step 1: Recall the Queue method for peeking

   In C#, the method to look at the front element without removing it is Peek().

2. Step 2: Verify method names

   Methods like Front(), GetFront(), or Top() do not exist in the standard Queue class.

3. Final Answer:

   myQueue.Peek(); -> Option C

4. Quick Check:

   Correct syntax is myQueue.Peek() [OK]

Hint: Use Peek() method to access front element [OK]

Common Mistakes:

• Using non-existent methods like Front()
• Confusing Peek() with Top() from stacks
• Missing parentheses after Peek

3. What will be the output of the following C# code?

Queue<int> q = new Queue<int>();
q.Enqueue(10);
q.Enqueue(20);
q.Enqueue(30);
Console.WriteLine(q.Peek());

medium

A. 10

B. 20

C. 30

D. Throws an exception

Solution

1. Step 1: Understand queue order after enqueues

   Elements are added in order: 10 (front), then 20, then 30 (back).

2. Step 2: Peek returns front element

   Calling Peek() returns the front element without removing it, which is 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Peek returns first enqueued element 10 [OK]

Hint: Peek returns first enqueued element [OK]

Common Mistakes:

• Thinking Peek returns last element
• Confusing Peek with Dequeue
• Assuming exception on non-empty queue

4. Identify the error in this code snippet that tries to peek the front element of a queue:

Queue<string> q = new Queue<string>();
string front = q.Peek;
Console.WriteLine(front);

medium

A. Peek method does not exist for Queue

B. Queue is empty, so Peek throws exception

C. Queue should be initialized with elements first

D. Missing parentheses after Peek method

Solution

1. Step 1: Check method call syntax

   The code uses q.Peek without parentheses, but Peek is a method and requires ().

2. Step 2: Confirm other possible errors

   Though the queue is empty, the question focuses on syntax. The missing parentheses cause a compile-time error.

3. Final Answer:

   Missing parentheses after Peek method -> Option D

4. Quick Check:

   Peek() needs parentheses to call method [OK]

Hint: Always add () when calling methods [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Ignoring empty queue exceptions
• Assuming Peek is a property

5. Given a queue q with elements [5, 10, 15], which code snippet correctly peeks the front element and then adds 20 to the queue without removing any elements?

hard

A. int front = q.Peek(); q.Enqueue(20);

B. int front = q.Dequeue(); q.Enqueue(20);

C. int front = q.Peek; q.Enqueue(20);

D. int front = q.Pop(); q.Enqueue(20);

Solution

1. Step 1: Identify correct method to peek front element

   Use Peek() to get front element without removing it.

2. Step 2: Add element without removing any

   Enqueue(20) adds 20 to the back without removing elements.

3. Step 3: Check other options for errors

   Dequeue() removes front element, Peek without parentheses is invalid, and Pop() does not exist for Queue.

4. Final Answer:

   int front = q.Peek(); q.Enqueue(20); -> Option A

5. Quick Check:

   Peek() + Enqueue() keeps queue intact [OK]

Hint: Peek() to view front, Enqueue() to add [OK]

Common Mistakes:

• Using Dequeue() instead of Peek() when not removing
• Missing parentheses on Peek
• Using Pop() which is for stacks