Queue vs Stack When to Use Which in DSA Rust - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Rust

queue.push_back([1]);

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

Aelement

Bpop_front()

Cpeek()

Dpush_front()

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop or peek methods instead of push_back.

Adding element to front instead of back.

To add an element to the end of a queue, use push_back() with the element as argument.

2fill in blank

medium

Complete the code to remove the top element from a stack.

DSA Rust

stack.[1]();

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

Aremove

Bpop_back

Cpop_front

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_back which does not exist on Vec.

Using pop_front which is for queues.

In Rust's Vec used as a stack, pop() removes the last element (top of stack).

3fill in blank

hard

Fix the error in the code to peek at the front element of a queue without removing it.

DSA Rust

let front = queue.[1]();

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

Apeek

Bpeek_front

Cfront

Dget_front

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'peek_front' which does not exist.

Using 'peek' or 'get_front' which are not standard methods.

Rust's VecDeque has a front() method to peek at the front element without removing it. It returns Option<&T>.

4fill in blank

hard

Fill both blanks to create a stack and add an element to it.

DSA Rust

let mut stack = Vec::[1]();
stack.[2](10);

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

Anew

Bpush

Cpop

Dwith_capacity

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push to add element.

Using with_capacity without adding elements.

To create a new empty stack, use Vec::new(). To add an element, use push().

5fill in blank

hard

Fill all three blanks to create a queue, add an element, and remove the front element.

DSA Rust

use std::collections::VecDeque;
let mut queue = VecDeque::[1]();
queue.[2](5);
let front = queue.[3]();

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

Anew

Bpush_back

Cpop_front

Dpush_front

Attempts:

3 left

💡 Hint

Common Mistakes

Using push_front to add element instead of push_back.

Using pop_back to remove front element.

Create a new queue with VecDeque::new(), add element with push_back(), and remove front element with pop_front().

Practice

1. Which data structure should you use when you want to process items in the exact order they arrive, like a line at a ticket counter?

easy

A. Queue

B. Stack

C. HashMap

D. Tree

Solution

1. Step 1: Understand the order requirement

   Processing items in the exact order they arrive means first-in, first-out (FIFO).

2. Step 2: Match order to data structure

   Queue follows FIFO, so it fits the requirement perfectly.

3. Final Answer:

   Queue -> Option A

4. Quick Check:

   FIFO = Queue [OK]

Hint: Use queue for first-in, first-out order [OK]

Common Mistakes:

• Choosing stack which is last-in, first-out
• Confusing queue with other data structures
• Ignoring the order requirement

2. Which Rust syntax correctly creates an empty stack using a vector?

easy

A. let mut stack: Vec<i32> = Vec::new();

B. let stack = Vec::empty();

C. let stack = new Vec<i32>();

D. let mut stack = Vec<i32>::init();

Solution

1. Step 1: Recall Rust vector creation syntax

   In Rust, Vec::new() creates an empty vector.

2. Step 2: Check mutability and type annotation

   Stack needs to be mutable to push/pop, and type must be specified or inferred.

3. Final Answer:

   let mut stack: Vec<i32> = Vec::new(); -> Option A

4. Quick Check:

   Vec::new() creates empty vector [OK]

Hint: Use Vec::new() with mut for stack in Rust [OK]

Common Mistakes:

• Using Vec::empty() which does not exist
• Using new keyword like other languages
• Missing mut keyword for modification

3. What will be the output of the following Rust code using a stack?

let mut stack = Vec::new();
stack.push(10);
stack.push(20);
stack.push(30);
while let Some(top) = stack.pop() {
    print!("{} ", top);
}

medium

A. 10 20 30

B. Compilation error

C. 30 20 10

D. 20 30 10

Solution

1. Step 1: Understand stack push order

   Items pushed: 10, then 20, then 30. Stack top is 30.

2. Step 2: Pop items prints in last-in, first-out order

   Pop removes 30 first, then 20, then 10, printing "30 20 10 ".

3. Final Answer:

   30 20 10 -> Option C

4. Quick Check:

   LIFO order = 30 20 10 [OK]

Hint: Stack pops in reverse order of pushes [OK]

Common Mistakes:

• Assuming FIFO order for stack
• Confusing push and pop order
• Expecting compilation error

4. The following Rust code tries to implement a queue using a vector. What is the main problem?

let mut queue = Vec::new();
queue.push(1);
queue.push(2);
queue.remove(0);
queue.remove(0);
println!("{:?}", queue);

medium

A. remove(0) causes a compilation error

B. Using remove(0) is inefficient for large queues

C. push() does not add elements to the vector

D. queue is immutable

Solution

1. Step 1: Understand vector remove(0) behavior

   remove(0) deletes first element but shifts all others left, costly for large vectors.

2. Step 2: Identify inefficiency in queue implementation

   Repeated remove(0) causes O(n) shifts, making it inefficient for queues.

3. Final Answer:

   Using remove(0) is inefficient for large queues -> Option B

4. Quick Check:

   remove(0) shifts elements = inefficient [OK]

Hint: remove(0) shifts all elements, slow for queues [OK]

Common Mistakes:

• Thinking remove(0) causes error
• Assuming push() does not add elements
• Ignoring performance impact

5. You need to design a system that processes tasks in the order they arrive but sometimes needs to undo the last task quickly. Which data structure combination is best in Rust?

hard

A. Use only a stack for both processing and undo

B. Use a HashMap to store tasks and undo

C. Use only a queue for both processing and undo

D. Use a queue for tasks and a stack for undo operations

Solution

1. Step 1: Understand processing order requirement

   Tasks must be processed in arrival order, so a queue (FIFO) is needed.

2. Step 2: Understand undo requirement

   Undo last task quickly means last-in, first-out order, so a stack fits undo.

3. Step 3: Combine data structures

   Use queue for normal processing and stack to track tasks for undo.

4. Final Answer:

   Use a queue for tasks and a stack for undo operations -> Option D

5. Quick Check:

   Queue for order + Stack for undo = Use a queue for tasks and a stack for undo operations [OK]

Hint: Queue for order, stack for undo actions [OK]

Common Mistakes:

• Using only stack loses arrival order
• Using only queue cannot undo last task easily
• Choosing HashMap which doesn't preserve order