Dequeue Operation in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to remove the first element from the deque.

DSA Rust

let mut deque = VecDeque::new();
deque.push_back(1);
deque.push_back(2);
let removed = deque.[1]();

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

Apop_back

Bpush_front

Cpop_front

Dpush_back

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_back() removes the last element instead of the first.

Using push_front() or push_back() adds elements instead of removing.

The pop_front() method removes and returns the first element from the deque.

2fill in blank

medium

Complete the code to add an element to the front of the deque.

DSA Rust

let mut deque = VecDeque::new();
deque.push_back(10);
deque.[1](5);

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

Apush_front

Bpop_front

Cpop_back

Dpush_back

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_front() or pop_back() which remove elements instead of adding.

Using push_back() which adds to the back, not the front.

The push_front() method adds an element to the front of the deque.

3fill in blank

hard

Fix the error in the code to correctly remove the last element from the deque.

DSA Rust

let mut deque = VecDeque::new();
deque.push_back(3);
deque.push_back(4);
let last = deque.[1]();

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

Apop_back

Bpop_front

Cpush_front

Dpush_back

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_front() removes the first element, not the last.

Using push_front() or push_back() adds elements instead of removing.

The pop_back() method removes and returns the last element from the deque.

4fill in blank

hard

Fill both blanks to add an element to the back and then remove the front element.

DSA Rust

let mut deque = VecDeque::new();
deque.[1](7);
let front = deque.[2]();

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

Apush_back

Bpop_front

Cpush_front

Dpop_back

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up push and pop methods.

Removing from the wrong end.

First, push_back() adds an element to the back. Then, pop_front() removes the front element.

5fill in blank

hard

Fill all three blanks to add elements to both ends and then remove the last element.

DSA Rust

let mut deque = VecDeque::new();
deque.[1](1);
deque.[2](2);
let last = deque.[3]();

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

Apush_front

Bpush_back

Cpop_back

Dpop_front

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_front() instead of pop_back() to remove last element.

Adding elements to wrong ends.

First, push_front() adds 1 to the front, push_back() adds 2 to the back, then pop_back() removes the last element.

Practice

1. What does the pop_front() operation do in a dequeue?

easy

A. Removes and returns the element at the front of the dequeue

B. Removes and returns the element at the back of the dequeue

C. Adds an element to the front of the dequeue

D. Adds an element to the back of the dequeue

Solution

1. Step 1: Understand pop_front() operation

   The pop_front() removes the first element from the front of the dequeue.

2. Step 2: Compare with other operations

   Unlike pop_back() which removes from the back, pop_front() targets the front element.

3. Final Answer:

   Removes and returns the element at the front of the dequeue -> Option A

4. Quick Check:

   pop_front() = remove front element [OK]

Hint: pop_front() always removes from the front [OK]

Common Mistakes:

• Confusing pop_front() with pop_back()
• Thinking pop_front() adds elements
• Mixing push and pop operations

2. Which of the following is the correct Rust syntax to remove an element from the back of a VecDeque named dq?

easy

A. dq.pop_front();

B. dq.pop_back();

C. dq.remove_back();

D. dq.pop();

Solution

1. Step 1: Identify VecDeque method for back removal

   The correct method to remove from the back is pop_back().

2. Step 2: Check other options

   pop_front() removes from front, remove_back() and pop() are invalid methods for VecDeque.

3. Final Answer:

   dq.pop_back(); -> Option B

4. Quick Check:

   pop_back() removes back element [OK]

Hint: Use pop_back() to remove from back in VecDeque [OK]

Common Mistakes:

• Using pop() which is for Vec, not VecDeque
• Using remove_back() which does not exist
• Confusing pop_front() with pop_back()

3. What is the output of the following Rust code?

use std::collections::VecDeque;

fn main() {
    let mut dq = VecDeque::new();
    dq.push_back(10);
    dq.push_back(20);
    dq.push_front(5);
    dq.pop_back();
    dq.push_front(1);
    println!("{:?}", dq);
}

medium

A. [5, 10, 20]

B. [1, 10, 20]

C. [10, 20, 1]

D. [1, 5, 10]

Solution

1. Step 1: Trace push_back and push_front calls

   After push_back(10) and push_back(20), dq = [10, 20]. Then push_front(5) makes dq = [5, 10, 20].

2. Step 2: Apply pop_back and push_front

   pop_back() removes 20, dq = [5, 10]. Then push_front(1) makes dq = [1, 5, 10].

3. Final Answer:

   [1, 5, 10] -> Option D

4. Quick Check:

   Operations result in [1, 5, 10] [OK]

Hint: Track each operation step-by-step on the deque [OK]

Common Mistakes:

• Forgetting pop_back removes last element
• Mixing order of push_front and push_back
• Misreading the final print format

4. Identify the error in this Rust code that tries to remove an element from the front of a VecDeque named dq:

use std::collections::VecDeque;

fn main() {
    let mut dq = VecDeque::new();
    dq.push_back(1);
    dq.push_back(2);
    let front = dq.pop();
    println!("{:?}", front);
}

medium

A. VecDeque has no method named pop()

B. pop() removes from back, not front

C. dq is not mutable

D. push_back() is used incorrectly

Solution

1. Step 1: Check VecDeque methods

   VecDeque does not have a method named pop(). It uses pop_front() or pop_back().

2. Step 2: Identify the error cause

   Calling dq.pop() causes a compile-time error because the method does not exist.

3. Final Answer:

   VecDeque has no method named pop() -> Option A

4. Quick Check:

   pop() method missing in VecDeque [OK]

Hint: Use pop_front() or pop_back() for VecDeque removals [OK]

Common Mistakes:

• Using pop() from Vec on VecDeque
• Ignoring compiler error messages
• Assuming pop() removes front element

5. Given a VecDeque with elements [3, 6, 9, 12], which sequence of operations will result in the dequeue [1, 3, 6]?

hard

A. dq.pop_back(); dq.pop_front(); dq.push_front(1);

B. dq.pop_front(); dq.pop_back(); dq.push_front(1);

C. dq.pop_back(); dq.pop_back(); dq.push_front(1);

D. dq.pop_front(); dq.pop_front(); dq.push_back(1);

Solution

1. Step 1: Start with dq = [3, 6, 9, 12]

   Initial dequeue has elements 3, 6, 9, 12 in order.

2. Step 2: Apply operations in dq.pop_back(); dq.pop_back(); dq.push_front(1);

   First pop_back() removes 12, dq = [3, 6, 9]. Second pop_back() removes 9, dq = [3, 6]. Then push_front(1) adds 1 at front, dq = [1, 3, 6].

3. Final Answer:

   dq.pop_back(); dq.pop_back(); dq.push_front(1); -> Option C

4. Quick Check:

   Operations produce [1, 3, 6] [OK]

Hint: Remove from back twice, then add 1 at front [OK]

Common Mistakes:

• Removing from front instead of back
• Adding 1 at back instead of front
• Wrong operation order