Queue Concept and FIFO Principle 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

queue.push_back([1]);

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

Aclear()

Bpop_front()

Cpeek()

Delement

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_front() instead of push_back()

Trying to peek instead of adding

Calling clear() which empties the queue

To add an element to the end of the queue, use push_back(element).

2fill in blank

medium

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

DSA Rust

let first = queue.[1]();

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

Apop_front

Bpush_back

Cpush_front

Dpop_back

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_back() which removes from the end

Using push_back() which adds instead of removes

Using push_front() which adds to the front

To remove the first element (front) of the queue, use pop_front().

3fill in blank

hard

Fix the error in the code to check if the queue is empty.

DSA Rust

if queue.[1]() { println!("Queue is empty"); }

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

Apop_front

Blen

Cis_empty

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using len() which returns a number, not a boolean

Using pop_front() which removes an element

Using clear() which empties the queue

Use is_empty() to check if the queue has no elements.

4fill in blank

hard

Fill both blanks to create a queue and add an element.

DSA Rust

let mut queue = VecDeque::new();
queue.[1]([2]);

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

Apush_back

Bpop_front

C42

Dpush_front

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop_front instead of push_back

Adding element with push_front which adds to front

Using a wrong value instead of 42

Create a new queue and add the number 42 to the back using push_back(42).

5fill in blank

hard

Fill all three blanks to remove and print the first element if the queue is not empty.

DSA Rust

if !queue.[1]() {
    let first = queue.[2]().unwrap();
    println!("First element: {}", [3]);
}

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

Ais_empty

Bpop_front

Cfirst

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using len() instead of is_empty() for condition

Using pop_back() instead of pop_front()

Printing queue instead of the removed element

Check if queue is not empty with is_empty(), remove first element with pop_front(), and print the variable first.

Practice

1. What does the FIFO principle mean in the context of a queue?

easy

A. First In, Last Out - the first element added is the last removed

B. Last In, Last Out - the last element added is the last removed

C. Last In, First Out - the last element added is the first removed

D. First In, First Out - the first element added is the first removed

Solution

1. Step 1: Understand FIFO principle

   FIFO means the first element added to the queue will be the first one to leave.

2. Step 2: Match FIFO with queue behavior

   Queues follow FIFO, so the first inserted element is removed first.

3. Final Answer:

   First In, First Out - the first element added is the first removed -> Option D

4. Quick Check:

   FIFO = First In, First Out [OK]

Hint: Remember queue = line; first come, first served [OK]

Common Mistakes:

• Confusing FIFO with LIFO
• Thinking queue removes last added first
• Mixing stack behavior with queue

2. Which of the following is the correct way to create an empty queue using Rust's standard library?

easy

A. let mut queue = Queue::new();

B. let mut queue = VecDeque::new();

C. let queue = Queue::empty();

D. let queue = Vec::queue();

Solution

1. Step 1: Identify Rust queue type

   Rust's standard library uses VecDeque for queue operations.

2. Step 2: Check correct syntax for empty VecDeque

   VecDeque::new() creates an empty queue correctly.

3. Final Answer:

   let mut queue = VecDeque::new(); -> Option B

4. Quick Check:

   VecDeque::new() creates empty queue [OK]

Hint: Use VecDeque::new() for empty queue in Rust [OK]

Common Mistakes:

• Using non-existent Queue::empty() method
• Confusing Vec with queue type
• Missing mut keyword for mutable queue

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

use std::collections::VecDeque;

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

medium

A. Some(10)
[20, 30]

B. Some(30)
[10, 20]

C. None
[10, 20, 30]

D. Some(20)
[10, 30]

Solution

1. Step 1: Trace queue insertions

   Elements 10, 20, 30 are added to the back in order.

2. Step 2: Pop front element

   pop_front() removes and returns the first element, which is 10.

3. Step 3: Print results

   first prints Some(10), queue now contains [20, 30].

4. Final Answer:

   Some(10) [20, 30] -> Option A

5. Quick Check:

   pop_front() returns first element [OK]

Hint: pop_front() removes first inserted element [OK]

Common Mistakes:

• Thinking pop_front() removes last element
• Confusing push_back with push_front
• Expecting None when queue is not empty

4. Identify the error in the following Rust code that tries to implement a queue using VecDeque:

use std::collections::VecDeque;

fn main() {
    let mut queue = VecDeque::new();
    queue.push_front(1);
    queue.push_back(2);
    let first = queue.pop_back();
    println!("{:?}", first);
}

medium

A. Error: push_front() is invalid method for VecDeque

B. No error; code works and prints Some(2)

C. Error: pop_back() should be pop_front() to follow FIFO

D. Error: queue must be immutable for pop_back()

Solution

1. Step 1: Analyze queue operations

   push_front(1) adds 1 at front, push_back(2) adds 2 at back.

2. Step 2: Check pop_back() usage

   pop_back() removes last element (2), but FIFO requires removing first element.

3. Step 3: Correct method for FIFO

   pop_front() should be used to remove the first inserted element.

4. Final Answer:

   Error: pop_back() should be pop_front() to follow FIFO -> Option C

5. Quick Check:

   FIFO needs pop_front(), not pop_back() [OK]

Hint: Use pop_front() to remove first element in queue [OK]

Common Mistakes:

• Using pop_back() instead of pop_front() for FIFO
• Thinking push_front() is invalid
• Forgetting mut keyword for mutable queue

5. You want to simulate a queue in Rust that processes tasks in order. Given this code snippet, what will be the final state of the queue after all operations?

use std::collections::VecDeque;

fn main() {
    let mut queue = VecDeque::new();
    queue.push_back("task1");
    queue.push_back("task2");
    queue.push_back("task3");
    queue.pop_front();
    queue.push_back("task4");
    queue.pop_front();
    println!("{:?}", queue);
}

hard

A. ["task3", "task4"]

B. ["task2", "task3", "task4"]

C. ["task1", "task4"]

D. ["task4"]

Solution

1. Step 1: Trace queue after initial pushes

   Queue after pushes: ["task1", "task2", "task3"]

2. Step 2: First pop_front()

   Removes "task1", queue: ["task2", "task3"]

3. Step 3: Push "task4"

   Queue: ["task2", "task3", "task4"]

4. Step 4: Second pop_front()

   Removes "task2", queue: ["task3", "task4"]

5. Final Answer:

   ["task3", "task4"] -> Option A

6. Quick Check:

   FIFO removes oldest tasks first [OK]

Hint: Pop front removes oldest; push back adds newest [OK]

Common Mistakes:

• Removing wrong elements with pop_back()
• Forgetting order of operations
• Assuming pop_front() removes last element