Stack vs Array Direct Use Why We Need Stack Abstraction in DSA Rust - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack using a vector.

DSA Rust

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

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

Apop

Bpush

Cinsert

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push will remove an element instead of adding.

Using insert or remove requires an index and is not typical for stack push.

The push method adds an element to the end of the vector, which acts like pushing onto a stack.

2fill in blank

medium

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

DSA Rust

let mut stack = vec![1, 2, 3];
let top = stack.[1]();

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

Apop

Bclear

Cremove

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using push will add an element instead of removing.

Using remove requires an index and is less safe for stack use.

The pop method removes and returns the last element of the vector, which is the top of the stack.

3fill in blank

hard

Fix the error in accessing the top element of the stack without removing it.

DSA Rust

let stack = vec![5, 6, 7];
let top = stack.[1]();

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

Alast

Bget

Cpop

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop removes the element, not just accesses it.

Using get requires an index and returns an Option.

The last method returns a reference to the last element without removing it, which is the top of the stack.

4fill in blank

hard

Fill both blanks to create a stack abstraction with push and pop methods.

DSA Rust

struct Stack<T> {
    elements: Vec<T>,
}

impl<T> Stack<T> {
    fn push(&mut self, item: T) {
        self.elements.[1](item);
    }

    fn pop(&mut self) -> Option<T> {
        self.elements.[2]()
    }
}

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

Apush

Bpop

Cinsert

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using insert or remove is not typical for stack push/pop.

Mixing up push and pop method names.

Using push adds an item to the vector, and pop removes the last item, implementing stack behavior.

5fill in blank

hard

Fill all three blanks to implement a method that checks if the stack is empty and returns its size.

DSA Rust

impl<T> Stack<T> {
    fn is_empty(&self) -> bool {
        self.elements.[1]()
    }

    fn size(&self) -> usize {
        self.elements.[2]()
    }

    fn clear(&mut self) {
        self.elements.[3]();
    }
}

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

Ais_empty

Blen

Cclear

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of clear will remove only one element.

Confusing len with is_empty.

is_empty checks if the vector has no elements, len returns the number of elements, and clear removes all elements.

Practice

1. Why do we prefer using a stack abstraction over directly using an array for stack operations?

easy

A. Because stack abstraction hides internal details and enforces correct usage

B. Because arrays are slower than stacks in all cases

C. Because arrays cannot store multiple data types

D. Because stack abstraction uses less memory than arrays

Solution

1. Step 1: Understand array direct use limitations

   Using arrays directly exposes internal details like indices and size, which can lead to incorrect usage such as accessing invalid positions.

2. Step 2: Benefits of stack abstraction

   Stack abstraction provides controlled access through push/pop methods, hiding internal details and preventing misuse.

3. Final Answer:

   Because stack abstraction hides internal details and enforces correct usage -> Option A

4. Quick Check:

   Stack abstraction = hides details, controls access [OK]

Hint: Stack abstraction controls access, arrays don't [OK]

Common Mistakes:

• Thinking arrays are always slower
• Confusing memory usage differences
• Believing arrays can't store multiple types

2. Which of the following Rust code snippets correctly pushes an element onto a stack implemented as a vector?

easy

A. stack.insert(5);

B. stack.add(5);

C. stack.push(5);

D. stack.append(5);

Solution

1. Step 1: Recall Rust vector push syntax

   In Rust, vectors use the method push() to add elements at the end.

2. Step 2: Check other options

   Methods add(), insert(), and append() either don't exist or have different signatures in Rust vectors.

3. Final Answer:

   stack.push(5); -> Option C

4. Quick Check:

   Rust vector push method = push() [OK]

Hint: Use push() to add elements to Rust vectors [OK]

Common Mistakes:

• Using add() which is not a Rust vector method
• Confusing insert() which requires index
• Using append() which expects another vector

3. What will be the output of this Rust code using a vector as a stack?

let mut stack = Vec::new();
stack.push(10);
stack.push(20);
let x = stack.pop();
println!("{:?}", stack);

medium

A. [20]

B. [10]

C. [10, 20]

D. []

Solution

1. Step 1: Trace push operations

   stack.push(10) adds 10, stack.push(20) adds 20, so stack is [10, 20].

2. Step 2: Trace pop operation

   stack.pop() removes and returns the last element 20, so stack becomes [10].

3. Final Answer:

   [10] -> Option B

4. Quick Check:

   Pop removes last element, stack left with [10] [OK]

Hint: Pop removes last pushed element from vector [OK]

Common Mistakes:

• Thinking pop removes first element
• Confusing push order
• Expecting stack unchanged after pop

4. Identify the error in this Rust code that tries to implement a stack using an array:

let mut stack: [i32; 3] = [0; 3];
stack.push(5);

medium

A. Array size must be dynamic to push elements

B. Array elements cannot be zero-initialized

C. Stack must be mutable to push elements

D. Arrays in Rust do not have a push method

Solution

1. Step 1: Check array methods in Rust

   Fixed-size arrays in Rust do not have a push() method because their size is fixed at compile time.

2. Step 2: Understand push method availability

   Only vectors (Vec) support push() to add elements dynamically.

3. Final Answer:

   Arrays in Rust do not have a push method -> Option D

4. Quick Check:

   Fixed arrays lack push() method [OK]

Hint: Only Vec supports push(), arrays do not [OK]

Common Mistakes:

• Thinking arrays can grow dynamically
• Confusing mutability with method availability
• Believing zero initialization prevents push

5. You want to implement a stack that can grow dynamically and prevent invalid access errors. Which Rust data structure and approach should you choose?

hard

A. Use a vector (Vec) with push and pop methods encapsulated in a Stack struct

B. Use a tuple to store elements and access by index

C. Use a linked list without any abstraction

D. Use a fixed-size array and manually track top index

Solution

1. Step 1: Consider dynamic growth requirement

   Fixed-size arrays cannot grow dynamically, so Use a fixed-size array and manually track top index is unsuitable.

2. Step 2: Consider safe access and abstraction

   Using a vector with push/pop inside a Stack struct provides dynamic size and controlled access, preventing invalid operations.

3. Step 3: Linked list without abstraction risks misuse

   Use a linked list without any abstraction lacks abstraction, increasing error risk.

4. Final Answer:

   Use a vector (Vec) with push and pop methods encapsulated in a Stack struct -> Option A

5. Quick Check:

   Dynamic stack with Vec and abstraction = Use a vector (Vec) with push and pop methods encapsulated in a Stack struct [OK]

Hint: Use Vec with Stack struct for safe dynamic stack [OK]

Common Mistakes:

• Choosing fixed arrays for dynamic needs
• Ignoring abstraction benefits
• Using tuples which are fixed size