Enqueue Operation in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an element to the end of the queue.

DSA Rust

fn enqueue(queue: &mut Vec<i32>, value: i32) {
    queue.[1](value);
}

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

Aremove

Bpop

Cpush

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push removes an element instead of adding.

Using insert requires an index and is not the simplest way to enqueue.

The push method adds an element to the end of the vector, which represents the queue.

2fill in blank

medium

Complete the code to check if the queue is empty before enqueueing.

DSA Rust

fn enqueue_if_not_empty(queue: &mut Vec<i32>, value: i32) {
    if !queue.[1]() {
        queue.push(value);
    }
}

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

Ais_empty

Blen

Cis_full

Dcontains

Attempts:

3 left

💡 Hint

Common Mistakes

Using len() without comparison does not return a boolean.

contains() checks for a value, not emptiness.

The is_empty method returns true if the vector has no elements. We use ! to check if it is not empty.

3fill in blank

hard

Fix the error in the enqueue function to correctly add an element.

DSA Rust

fn enqueue(queue: &mut Vec<i32>, value: i32) {
    queue.[1](value);
}

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

Apop

Bpush

Cremove

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop removes the last element instead of adding.

Using remove requires an index and removes an element.

The push method correctly adds an element to the end of the vector. Using pop or remove removes elements, which is incorrect for enqueue.

4fill in blank

hard

Fill both blanks to create a function that enqueues only if the queue size is less than max_size.

DSA Rust

fn enqueue_with_limit(queue: &mut Vec<i32>, value: i32, max_size: usize) {
    if queue.[1]() < max_size {
        queue.[2](value);
    }
}

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

Alen

Bpop

Cpush

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push removes elements.

Using clear empties the queue.

We check the current length of the queue with len() and add the new value using push() if the size limit is not reached.

5fill in blank

hard

Fill all three blanks to create a function that enqueues a value only if it is not already in the queue and the queue is not full.

DSA Rust

fn enqueue_unique(queue: &mut Vec<i32>, value: i32, max_size: usize) {
    if !queue.[1](&value) && queue.[2]() < max_size {
        queue.[3](value);
    }
}

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

Acontains

Blen

Cpush

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove instead of push removes elements.

Not checking if the value already exists causes duplicates.

The function checks if the value is not already in the queue using contains, then checks if the queue size is less than max_size using len(), and finally adds the value with push().

Practice

1. What does the enqueue operation do in a queue data structure?

easy

A. Returns the number of elements in the queue

B. Removes an element from the front of the queue

C. Checks if the queue is empty

D. Adds an element to the end of the queue

Solution

1. Step 1: Understand queue behavior

   A queue works like a line where new people join at the end.

2. Step 2: Define enqueue operation

   Enqueue means adding a new element at the back of the queue.

3. Final Answer:

   Adds an element to the end of the queue -> Option D

4. Quick Check:

   Enqueue = Add at end [OK]

Hint: Enqueue always adds at the back of the queue [OK]

Common Mistakes:

• Confusing enqueue with dequeue
• Thinking enqueue removes elements
• Mixing enqueue with checking queue size

2. Which of the following is the correct Rust syntax to enqueue an element 5 into a queue implemented as a VecDeque named queue?

easy

A. queue.push_front(5);

B. queue.enqueue(5);

C. queue.push_back(5);

D. queue.insert(5);

Solution

1. Step 1: Identify VecDeque enqueue method

   In Rust, VecDeque uses push_back to add elements at the end.

2. Step 2: Check options for correct method

   Only queue.push_back(5); correctly adds 5 at the back.

3. Final Answer:

   queue.push_back(5); -> Option C

4. Quick Check:

   VecDeque enqueue = push_back [OK]

Hint: Use push_back to enqueue in VecDeque [OK]

Common Mistakes:

• Using push_front instead of push_back
• Using non-existent enqueue method
• Using insert without index

3. What will be the output of the following Rust code snippet?

use std::collections::VecDeque;

fn main() {
    let mut queue = VecDeque::new();
    queue.push_back(10);
    queue.push_back(20);
    queue.push_back(30);
    queue.push_back(40);
    println!("{:?}", queue);
}

medium

A. [10, 20, 30, 40]

B. [40, 30, 20, 10]

C. [10, 20, 30]

D. Compilation error

Solution

1. Step 1: Trace enqueue operations

   Elements 10, 20, 30, 40 are added in order at the back of the queue.

2. Step 2: Understand VecDeque print format

   Printing the queue shows elements in insertion order inside square brackets.

3. Final Answer:

   [10, 20, 30, 40] -> Option A

4. Quick Check:

   Enqueue order preserved in VecDeque [OK]

Hint: VecDeque prints elements in insertion order [OK]

Common Mistakes:

• Assuming push_back adds at front
• Confusing output order
• Expecting compilation error

4. Identify the error in the following Rust code that tries to enqueue an element into a queue:

use std::collections::VecDeque;

fn main() {
    let mut queue = VecDeque::new();
    queue.enqueue(15);
    println!("{:?}", queue);
}

medium

A. VecDeque cannot store integers directly

B. VecDeque has no method named 'enqueue'

C. println! macro syntax is incorrect

D. Missing 'mut' keyword for queue variable

Solution

1. Step 1: Check VecDeque methods

   VecDeque does not have an 'enqueue' method; it uses 'push_back' to add elements.

2. Step 2: Verify other code parts

   The queue is mutable and println! syntax is correct; VecDeque supports integers.

3. Final Answer:

   VecDeque has no method named 'enqueue' -> Option B

4. Quick Check:

   Use push_back, not enqueue [OK]

Hint: VecDeque uses push_back, not enqueue [OK]

Common Mistakes:

• Using enqueue method on VecDeque
• Forgetting mut keyword (not error here)
• Misreading println! syntax

5. You want to implement a queue using a Rust Vec where enqueue adds elements at the end and dequeue removes from the front. Which of the following code snippets correctly enqueues the element 7?

hard

A. queue.push(7);

B. queue.insert(0, 7);

C. queue.remove(0); queue.push(7);

D. queue.pop(); queue.push(7);

Solution

1. Step 1: Understand enqueue in Vec-based queue

   Enqueue means adding at the end, so push adds element at the back.

2. Step 2: Analyze options

   queue.push(7); uses push(7) which correctly adds 7 at the end. Others either insert at front or remove elements.

3. Final Answer:

   queue.push(7); -> Option A

4. Quick Check:

   Vec enqueue = push at end [OK]

Hint: Use push to enqueue in Vec-based queue [OK]

Common Mistakes:

• Using insert(0, val) which adds at front
• Removing elements before enqueue
• Using pop which removes last element