Node Structure and Pointer Design in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a struct for a singly linked list node with an integer value and a next pointer.

DSA Rust

struct Node {
    value: i32,
    next: Option<Box<[1]>>,
}

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

AOption

BNode

CBox

Di32

Attempts:

3 left

💡 Hint

Common Mistakes

Using raw pointers instead of Box

Forgetting to wrap the next pointer in Option

Using the wrong type inside Box

The next field must be an Option wrapping a Box pointing to the same Node type to allow recursive definition.

2fill in blank

medium

Complete the code to create a new node with value 10 and no next node.

DSA Rust

let node = Node {
    value: 10,
    next: [1],
};

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

ANone

BSome(Box::new(Node { value: 0, next: None }))

CBox::new(None)

DSome(10)

Attempts:

3 left

💡 Hint

Common Mistakes

Using Some with invalid values

Trying to box None

Assigning a raw value instead of Option

The next pointer should be None to indicate the end of the list.

3fill in blank

hard

Fix the error in the code to link two nodes correctly.

DSA Rust

let second = Node { value: 20, next: None };
let first = Node {
    value: 10,
    next: [1],
};

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

ASome(Box::new(second))

BSome(second)

CBox::new(second)

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using Some without boxing

Using Box without Some

Assigning None by mistake

The next field requires an Option>. So we must box the second node and wrap it in Some.

4fill in blank

hard

Fill both blanks to implement a method that returns the value of the next node if it exists.

DSA Rust

impl Node {
    fn next_value(&self) -> Option<i32> {
        self.next.as_ref().map(|[1]| *[2].value)
    }
}

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

Anode

Bn

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names

Trying to dereference incorrectly

Returning the node instead of its value

The closure argument can be named anything, here n is used. Then we access *n.value to get the next node's value.

5fill in blank

hard

Fill all three blanks to implement a method that appends a new node with given value at the end of the list.

DSA Rust

impl Node {
    fn append(&mut self, val: i32) {
        let mut current = self;
        while let Some(ref mut [1]) = current.[2] {
            current = [3];
        }
        current.next = Some(Box::new(Node { value: val, next: None }));
    }
}

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

Anext_node

Bnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using immutable references instead of mutable

Incorrect variable names causing borrow errors

Not updating current inside the loop

We use next_node as the mutable reference name to the next node, access current.next, and then update current to next_node to traverse the list.

Practice

1. What is the primary purpose of a next pointer in a singly linked list node structure?

easy

A. To indicate the size of the list

B. To store the data value of the node

C. To point to the next node in the list

D. To point to the previous node in the list

Solution

1. Step 1: Understand the role of pointers in linked lists

   In a singly linked list, each node contains data and a pointer to the next node to maintain the sequence.

2. Step 2: Identify the function of the next pointer

   The next pointer specifically points to the next node, enabling traversal through the list.

3. Final Answer:

   To point to the next node in the list -> Option C

4. Quick Check:

   next pointer = next node address [OK]

Hint: Next pointer always links to the following node [OK]

Common Mistakes:

• Confusing next pointer with previous pointer
• Thinking next stores data instead of address
• Assuming next pointer stores list size

2. Which of the following is the correct Rust syntax to define a singly linked list node struct with a next pointer using Option and Box?

easy

A. struct Node { data: i32, next: Option }

B. struct Node { data: i32, next: &Node }

C. struct Node { data: i32, next: Box<Node> }

D. struct Node { data: i32, next: Option<&Node> }

Solution

1. Step 1: Recall Rust ownership and pointer rules for linked lists

   Rust requires heap allocation for recursive types, so Box is used to allocate nodes on the heap. The Option type allows for a nullable pointer.

2. Step 2: Analyze each option's correctness

   struct Node { data: i32, next: Box<Node> } lacks Option, so it cannot represent the end of the list (null). struct Node { data: i32, next: Option } correctly uses Option. struct Node { data: i32, next: &Node } uses a reference without lifetime, which is invalid. struct Node { data: i32, next: Option<&Node> } uses a reference inside Option, which is problematic for ownership.

3. Final Answer:

   struct Node { data: i32, next: Option } -> Option A

4. Quick Check:

   Use Option for nullable heap pointer [OK]

Hint: Use Option for nullable next pointer in Rust [OK]

Common Mistakes:

• Omitting Option to represent null
• Using references without lifetimes
• Not boxing recursive types

3. Given the following Rust code for a singly linked list node, what will be printed?

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

fn main() {
    let node3 = Node { data: 3, next: None };
    let node2 = Node { data: 2, next: Some(Box::new(node3)) };
    let node1 = Node { data: 1, next: Some(Box::new(node2)) };

    let mut current = &node1;
    while let Some(ref next_node) = current.next {
        println!("{} ->", current.data);
        current = next_node;
    }
    println!("{} -> null", current.data);
}

medium

A. 1 -> 2 -> 3 -> null

B. 3 -> 2 -> 1 -> null

C. 1 -> 2 -> null

D. Compilation error due to ownership

Solution

1. Step 1: Trace the linked list construction

   node1 points to node2, node2 points to node3, node3 points to None (end).

2. Step 2: Follow the while loop printing data

   The loop prints current.data and moves to next node until next is None. It prints 1, then 2, then 3, then prints 3 -> null after loop.

3. Final Answer:

   1 -> 2 -> 3 -> null -> Option A

4. Quick Check:

   Traverse nodes in order: 1, 2, 3 [OK]

Hint: Follow next pointers from head to end [OK]

Common Mistakes:

• Confusing order of nodes
• Expecting reverse print
• Thinking ownership causes compile error here

4. Identify the error in this Rust code snippet defining a linked list node:

struct Node {
    data: i32,
    next: Option<Node>,
}

medium

A. Data type i32 is invalid for node data

B. Missing Box to allocate next node on heap

C. Option cannot be used with structs

D. next should be a reference &Node instead

Solution

1. Step 1: Understand recursive struct requirements in Rust

   Rust needs recursive types to use indirection like Box to know size at compile time.

2. Step 2: Analyze the next field type

   Using Option<Node> causes infinite size because Node contains Node directly. It must be Option to compile.

3. Final Answer:

   Missing Box to allocate next node on heap -> Option B

4. Quick Check:

   Recursive structs need Box for next pointer [OK]

Hint: Use Box for recursive node pointers in Rust [OK]

Common Mistakes:

• Omitting Box causes compile error
• Using references without lifetimes
• Thinking Option<Node> is enough

5. You want to design a doubly linked list node in Rust with safe ownership. Which of the following node struct definitions correctly uses pointers to represent prev and next nodes without causing ownership or borrowing errors?

hard

A. struct Node { data: i32, prev: Option, next: Option }

B. struct Node { data: i32, prev: Option<&Node>, next: Option<&Node> }

C. struct Node { data: i32, prev: Option<*mut Node>, next: Option }

D. struct Node { data: i32, prev: Option>, next: Option> }

Solution

1. Step 1: Understand ownership challenges in doubly linked lists

   Doubly linked lists have nodes pointing both ways, causing multiple ownership which Rust's default ownership model disallows.

2. Step 2: Analyze pointer types for safe shared ownership

   struct Node { data: i32, prev: Option, next: Option } uses Box for both prev and next, causing ownership conflicts. struct Node { data: i32, prev: Option<*mut Node>, next: Option } uses raw pointer for prev, unsafe. struct Node { data: i32, prev: Option<&Node>, next: Option<&Node> } uses references without lifetimes, invalid. struct Node { data: i32, prev: Option>, next: Option> } uses Rc allowing multiple owners and interior mutability safely.

3. Final Answer:

   struct Node { data: i32, prev: Option>, next: Option> } -> Option D

4. Quick Check:

   Use Rc and RefCell for safe shared mutable ownership [OK]

Hint: Use Rc for doubly linked list nodes [OK]

Common Mistakes:

• Using Box for both prev and next causes ownership errors
• Using raw pointers without safety
• Using references without lifetimes