Tree vs Array vs Linked List When Hierarchy Matters in DSA Rust - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple array of integers.

DSA Rust

let numbers = [1, 2, 3, 4, [1]];

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

A6

B7

C8

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number not matching the sequence.

Leaving the blank empty.

The array ends with the number 5, so the blank should be filled with 5.

2fill in blank

medium

Complete the code to create a linked list node with a value.

DSA Rust

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

let node = Node { value: [1], next: None };

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

A20

B10

C30

D40

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value not matching the example.

Confusing next with value.

The node's value is set to 20 as per the example.

3fill in blank

hard

Fix the error in the tree node creation by filling the correct child node value.

DSA Rust

struct TreeNode {
    value: i32,
    left: Option<Box<TreeNode>>,
    right: Option<Box<TreeNode>>,
}

let root = TreeNode {
    value: 1,
    left: Some(Box::new(TreeNode { value: [1], left: None, right: None })),
    right: None,
};

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

A3

B2

C4

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value other than 2 for the left child.

Leaving the child node value blank.

The left child node value is 2 to maintain the example tree structure.

4fill in blank

hard

Fill both blanks to create a linked list node that points to another node.

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))

BNone

CSome(Box::new(first))

DBox::new(second)

Attempts:

3 left

💡 Hint

Common Mistakes

Using None instead of Some(Box::new(...)).

Not boxing the node.

The first node's next points to the second node wrapped in Some and Box.

5fill in blank

hard

Fill all three blanks to create a tree node with left and right children.

DSA Rust

let left_child = TreeNode { value: [1], left: None, right: None };
let right_child = TreeNode { value: [2], left: None, right: None };
let root = TreeNode {
    value: [3],
    left: Some(Box::new(left_child)),
    right: Some(Box::new(right_child)),
};

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

A2

B3

C1

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping left and right child values.

Using root value same as children.

Left child is 2, right child is 3, root is 1 to form a simple tree.

Practice

1. Which data structure is best to represent a hierarchy where each element can have multiple children, like a company organizational chart?

easy

A. Stack

B. Array

C. Linked List

D. Tree

Solution

1. Step 1: Understand hierarchy representation

   A hierarchy with multiple children per element needs a structure that can link one parent to many children.

2. Step 2: Compare data structures

   Arrays and linked lists are linear and do not naturally represent multiple children. Trees allow each node to have multiple children, fitting the hierarchy.

3. Final Answer:

   Tree -> Option D

4. Quick Check:

   Hierarchy with multiple children = Tree [OK]

Hint: Use trees for multi-child hierarchies, arrays for flat data [OK]

Common Mistakes:

• Choosing array for hierarchical data
• Using linked list which is linear
• Confusing stack with hierarchy

2. Which of the following Rust code snippets correctly declares a linked list node struct with a value and a next pointer?

easy

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

B. struct Node { value: i32, next: Node }

C. struct Node { value: i32, next: &Node }

D. struct Node { value: i32, next: Vec<Node> }

Solution

1. Step 1: Understand Rust linked list node

   Linked list nodes need a pointer to the next node. Rust uses Option for nullable heap pointers.

2. Step 2: Check each option

   A uses direct Node which causes infinite size error. C uses reference without lifetime. D uses Vec which is for multiple children, not linked list.

3. Final Answer:

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

4. Quick Check:

   Linked list node uses Option [OK]

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

Common Mistakes:

• Using direct Node type causing infinite size
• Using references without lifetimes
• Using Vec instead of single next pointer

3. What will be the output of this Rust code that builds a simple tree and prints the root's first child's value?

struct Node {
    value: i32,
    children: Vec<Node>,
}

fn main() {
    let child = Node { value: 10, children: vec![] };
    let root = Node { value: 5, children: vec![child] };
    println!("{}", root.children[0].value);
}

medium

A. 10

B. 5

C. 0

D. Compilation error

Solution

1. Step 1: Understand tree structure and initialization

   Root node has value 5 and one child with value 10 stored in a vector.

2. Step 2: Trace the print statement

   Printing root.children[0].value accesses the first child's value, which is 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   root.children[0].value = 10 [OK]

Hint: Access first child value with root.children[0].value [OK]

Common Mistakes:

• Printing root.value instead of child's
• Confusing vector index
• Assuming compilation error due to struct

4. This Rust code tries to create a linked list but fails to compile. What is the main error?

struct Node {
    value: i32,
    next: Box<Node>,
}

fn main() {
    let node = Node { value: 1, next: Box::new(Node { value: 2, next: Box::new(Node { value: 3, next: None }) }) };
}

medium

A. Value type i32 is invalid

B. Missing Option for next pointer to allow None

C. Box cannot be used for recursive types

D. Syntax error in struct definition

Solution

1. Step 1: Identify recursive type issue

   Recursive types in Rust must use Option to allow end of list (None).

2. Step 2: Check code for missing Option

   Code uses Box<Node> without Option, so no way to represent end (None), causing compile error.

3. Final Answer:

   Missing Option for next pointer to allow None -> Option B

4. Quick Check:

   Recursive next pointer needs Option [OK]

Hint: Use Option for nullable next in linked list [OK]

Common Mistakes:

• Thinking Box alone handles recursion
• Blaming i32 type
• Assuming syntax error in struct

5. You want to represent a file system hierarchy in Rust where folders can contain files and other folders. Which data structure and Rust type combination is best suited for this?

hard

A. Array of strings

B. Linked list of file names

C. Tree with enum Node { File(String), Folder(Vec<Node>) }

D. HashMap with file paths as keys

Solution

1. Step 1: Understand file system hierarchy

   Folders can contain files and other folders, so a recursive structure is needed.

2. Step 2: Evaluate data structure options

   Array or linked list can't represent nested folders well. HashMap stores flat keys, not hierarchy. Tree with enum Node allows files and folders recursively.

3. Final Answer:

   Tree with enum Node { File(String), Folder(Vec<Node>) } -> Option C

4. Quick Check:

   Recursive enum tree fits file system hierarchy [OK]

Hint: Use recursive enum tree for nested folders and files [OK]

Common Mistakes:

• Using flat arrays or lists for nested folders
• Using HashMap which is flat key-value
• Not using enum to distinguish files and folders