Stack Using Linked List vs Array Stack Trade-offs in DSA Rust - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the array-based stack.

DSA Rust

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

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

Ainsert

Bpush

Cappend

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which is for adding another vector, not a single element.

Using 'insert' which requires an index.

In Rust, Vec uses push to add elements at the end.

2fill in blank

medium

Complete the code to pop an element from the linked list stack.

DSA Rust

fn pop(head: &mut Option<Box<Node>>) -> Option<i32> {
    if let Some(node) = head.take() {
        *head = node.next;
        return Some(node.[1]);
    }
    None
}

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

Adata

Bval

Cvalue

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect field names like 'data' or 'val' which do not exist.

The linked list node stores the element in the field named value.

3fill in blank

hard

Fix the error in the linked list push function by completing the blank.

DSA Rust

fn push(head: &mut Option<Box<Node>>, value: i32) {
    let new_node = Box::new(Node {
        value,
        next: [1],
    });
    *head = Some(new_node);
}

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

Ahead.next

Bhead

Chead.clone()

D*head

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head' directly which is a mutable reference, not the node.

Using 'head.clone()' which clones the Option but is unnecessary here.

The new node's next should point to the current head, which is *head.

4fill in blank

hard

Fill both blanks to create a function that checks if the array stack is empty.

DSA Rust

fn is_empty(stack: &Vec<i32>) -> bool {
    stack.[1]() == [2]
}

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

Alen

B0

Cis_empty

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'is_empty() == None' which is incorrect because is_empty returns bool.

Comparing length to None which is not a number.

Check if the length of the vector is zero to know if the stack is empty.

5fill in blank

hard

Fill all three blanks to create a function that returns the top element of the linked list stack without removing it.

DSA Rust

fn peek(head: &Option<Box<Node>>) -> Option<i32> {
    match head {
        Some(node) => Some(node.[1]),
        None => [2],
    }
}

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

Avalue

BNone

CSome(0)

Dnode.value

Attempts:

3 left

💡 Hint

Common Mistakes

Returning Some(0) for empty stack which is incorrect.

Using 'node.value' outside the match arm.

Return the value if the node exists, otherwise return None.

Practice

1. Which of the following is a key advantage of using a linked list to implement a stack compared to using an array?

easy

A. Faster access to elements by index

B. Simpler to implement in all languages

C. Uses less memory overall

D. Dynamic size without needing to resize

Solution

1. Step 1: Understand stack size behavior

   Arrays have fixed size or require resizing, linked lists grow dynamically as needed.

2. Step 2: Compare access and memory

   Linked lists do not provide faster index access and may use more memory due to pointers.

3. Final Answer:

   Dynamic size without needing to resize -> Option D

4. Quick Check:

   Linked list stacks grow dynamically = B [OK]

Hint: Linked list stacks grow dynamically, arrays need resizing [OK]

Common Mistakes:

• Thinking linked lists have faster index access
• Assuming arrays always use less memory
• Believing linked lists are simpler to implement everywhere

2. Which Rust syntax correctly declares a stack using a vector (array stack)?

easy

A. let stack: Vec<i32> = [];

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

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

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

Solution

1. Step 1: Recall Rust vector initialization

   Correct syntax uses Vec::new() to create an empty vector.

2. Step 2: Check each option

   B uses invalid 'new' keyword, C uses array syntax, D uses non-existent empty() method.

3. Final Answer:

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

4. Quick Check:

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

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

Common Mistakes:

• Using 'new' keyword instead of Vec::new()
• Trying to assign array literal directly
• Using non-existent Vec methods

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

struct Node {
    value: i32,
    next: Option,
}

fn main() {
    let mut stack: Option = None;
    // Push 10
    stack = Some(Box::new(Node { value: 10, next: stack }));
    // Push 20
    stack = Some(Box::new(Node { value: 20, next: stack }));
    // Pop top
    if let Some(top) = stack {
        println!("{}", top.value);
        stack = top.next;
    }
    // Print new top
    if let Some(top) = &stack {
        println!("{}", top.value);
    }
}

medium

A. 20
10

B. 10
20

C. 10
10

D. 20
20

Solution

1. Step 1: Trace push operations

   Push 10: stack points to node with value 10. Push 20: stack points to node with value 20, next points to 10.

2. Step 2: Trace pop and prints

   Pop prints 20, then stack moves to next node (10). Next print prints 10.

3. Final Answer:

   20 10 -> Option A

4. Quick Check:

   Stack top after push: 20, after pop: 10 [OK]

Hint: Top is last pushed, pop removes top, next is previous [OK]

Common Mistakes:

• Confusing push order and print order
• Printing after pop without updating stack
• Misunderstanding Option and Box usage

4. Identify the bug in this Rust code implementing a stack with an array (Vec) and fix it:

fn main() {
    let mut stack: Vec<i32> = Vec::new();
    stack.push(1);
    stack.push(2);
    let top = stack.pop();
    println!("Top element: {}", top.unwrap());
    println!("Next element: {}", stack.pop().unwrap());
    println!("Empty pop: {}", stack.pop().unwrap());
}

medium

A. Calling unwrap() on empty pop causes panic; check Option before unwrap

B. Vec::new() should be Vec::with_capacity()

C. Use stack.peek() instead of pop() to view top

D. stack.push() should be called after pop()

Solution

1. Step 1: Analyze pop calls and unwrap

   First two pops succeed, third pop returns None; unwrap on None panics.

2. Step 2: Fix by checking Option before unwrap

   Use if let or match to safely handle empty stack before unwrap.

3. Final Answer:

   Calling unwrap() on empty pop causes panic; check Option before unwrap -> Option A

4. Quick Check:

   Pop returns Option, unwrap on None panics [OK]

Hint: Always check Option before unwrap after pop [OK]

Common Mistakes:

• Ignoring possibility of empty stack pop
• Thinking Vec::with_capacity fixes panic
• Using peek instead of pop changes logic

5. You need to implement a stack in Rust for a program where the maximum number of elements is unknown and can grow large unpredictably. Which implementation is better and why?

1. Array stack using Vec with occasional resizing
2. Linked list stack with dynamic nodes

hard

A. Array stack is better because it uses less memory per element and faster cache access

B. Linked list stack is better because it grows dynamically without resizing overhead

C. Array stack is better because resizing never happens in Rust Vec

D. Linked list stack is better because it uses contiguous memory for faster access

Solution

1. Step 1: Consider unknown large size and growth

   Linked list stacks grow node by node without resizing, arrays resize which can be costly.

2. Step 2: Compare memory and speed trade-offs

   Arrays have better cache but resizing overhead; linked lists avoid resizing but use extra memory per node.

3. Step 3: Choose best fit for unpredictable large growth

   Linked list avoids resizing delays and can handle unpredictable growth smoothly.

4. Final Answer:

   Linked list stack is better because it grows dynamically without resizing overhead -> Option B

5. Quick Check:

   Dynamic growth without resizing = Linked list stack [OK]

Hint: For unknown large size, linked list avoids resizing delays [OK]

Common Mistakes:

• Assuming Vec never resizes
• Ignoring memory overhead of linked list nodes
• Confusing contiguous memory with linked list