Why Trees Exist and What Linked Lists and Arrays Cannot Do in DSA Rust - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new tree node with a value.

DSA Rust

struct TreeNode {
    value: i32,
    children: Vec<Box<TreeNode>>,
}

impl TreeNode {
    fn new(val: i32) -> Box<Self> {
        Box::new(TreeNode {
            value: [1],
            children: Vec::new(),
        })
    }
}

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

Anew

Bvalue

Cval

Dchildren

Attempts:

3 left

💡 Hint

Common Mistakes

Using the field name 'value' instead of the parameter 'val'.

Trying to assign 'children' here.

The constructor takes val as input and assigns it to the value field.

2fill in blank

medium

Complete the code to add a child node to a tree node.

DSA Rust

impl TreeNode {
    fn add_child(&mut self, child: Box<TreeNode>) {
        self.children.[1](child);
    }
}

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

Ainsert

Bextend

Cappend

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using extend() which expects an iterator.

Using insert() without an index.

Vec uses push() to add a single element at the end.

3fill in blank

hard

Fix the error in the code to check if a tree node has children.

DSA Rust

impl TreeNode {
    fn has_children(&self) -> bool {
        self.children.[1]() > 0
    }
}

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

Alen

Blength

Csize

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using length() which is not a Vec method.

Using size() or count() which do not exist for Vec.

Vec in Rust uses len() to get the number of elements.

4fill in blank

hard

Fill both blanks to create a tree node and add a child.

DSA Rust

let mut root = TreeNode::[1](10);
root.children.[2](TreeNode::new(20));

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

Anew

Bpush

Cinsert

Dextend

Attempts:

3 left

💡 Hint

Common Mistakes

Using insert() without index.

Using extend() to add a single child.

Use new() to create a node and push() to add a child.

5fill in blank

hard

Fill all three blanks to create a tree, add children, and check if root has children.

DSA Rust

let mut root = TreeNode::[1](5);
root.children.[2](TreeNode::new(15));
let has_kids = root.children.[3]() > 0;

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

Anew

Bpush

Clen

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using insert() without index.

Using size() or length() instead of len().

Create with new(), add child with push(), check length with len().

Practice

1. Why do trees exist as a data structure when we already have arrays and linked lists?

easy

A. Because trees allow hierarchical data representation which arrays and linked lists cannot efficiently provide

B. Because trees use less memory than arrays and linked lists

C. Because trees are easier to implement than arrays and linked lists

D. Because trees always have faster access time than arrays

Solution

1. Step 1: Understand the limitation of arrays and linked lists

   Arrays and linked lists store data linearly, which makes representing hierarchical relationships difficult and inefficient.

2. Step 2: Identify the advantage of trees

   Trees naturally represent hierarchical data with parent-child relationships, enabling efficient searching and organization of such data.

3. Final Answer:

   Trees allow hierarchical data representation which arrays and linked lists cannot efficiently provide -> Option A

4. Quick Check:

   Hierarchical data needs trees [OK]

Hint: Trees represent hierarchy; arrays and lists are linear [OK]

Common Mistakes:

• Thinking trees always use less memory
• Assuming trees are simpler to implement
• Believing trees always have faster access than arrays

2. Which of the following is the correct way to define a simple binary tree node struct in Rust?

easy

A. struct Node { value: i32, left: Option, right: Option }

B. struct Node { value: i32, left: Node, right: Node }

C. struct Node { value: i32, left: &Node, right: &Node }

D. struct Node { value: i32, left: Box<Node>, right: Box<Node> }

Solution

1. Step 1: Understand Rust ownership and recursive types

   Recursive types like trees need indirection (Box) and optional to allow empty children.

2. Step 2: Check each option

   struct Node { value: i32, left: Option, right: Option } uses Option for left and right, which is correct. struct Node { value: i32, left: Node, right: Node } is invalid because it causes infinite size. struct Node { value: i32, left: &Node, right: &Node } uses references without lifetimes. struct Node { value: i32, left: Box<Node>, right: Box<Node> } lacks Option, so no empty child allowed.

3. Final Answer:

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

4. Quick Check:

   Recursive structs need Option [OK]

Hint: Use Option for recursive tree nodes in Rust [OK]

Common Mistakes:

• Defining child nodes without Box causing infinite size
• Using references without lifetimes
• Not using Option for nullable children

3. What will be the output of the following Rust code that builds a simple binary tree and prints the root value?

struct Node {
    value: i32,
    left: Option,
    right: Option,
}

fn main() {
    let root = Node {
        value: 10,
        left: Some(Box::new(Node { value: 5, left: None, right: None })),
        right: Some(Box::new(Node { value: 15, left: None, right: None })),
    };
    println!("{}", root.value);
}

medium

A. 15

B. 5

C. 10

D. Compilation error

Solution

1. Step 1: Analyze the tree construction

   The root node is created with value 10, left child 5, right child 15.

2. Step 2: Check the printed value

   The code prints root.value, which is 10.

3. Final Answer:

   10 -> Option C

4. Quick Check:

   Print root.value = 10 [OK]

Hint: Print root.value to get 10 [OK]

Common Mistakes:

• Confusing child values with root value
• Expecting print of left or right child
• Assuming compilation error due to Option usage

4. The following Rust code tries to create a binary tree node but fails to compile. What is the error?

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

fn main() {
    let root = Node {
        value: 1,
        left: Box::new(Node { value: 2, left: Box::new(Node { value: 3, left: None, right: None }), right: None }),
        right: Box::new(Node { value: 4, left: None, right: None }),
    };
}

medium

A. Cannot use None for Box<Node> fields; should use Option

B. Missing semicolon after struct definition

C. Box cannot be used inside structs

D. Cannot create nested structs in Rust

Solution

1. Step 1: Identify the field types and assigned values

   The struct fields left and right are Box<Node>, but code assigns None to some of them.

2. Step 2: Understand why None is invalid here

   None is an Option variant, but fields are Box<Node> (non-optional), so None cannot be assigned.

3. Final Answer:

   Cannot use None for Box<Node> fields; should use Option -> Option B

4. Quick Check:

   Use Option for nullable children [OK]

Hint: Use Option to allow None children [OK]

Common Mistakes:

• Thinking Box<Node> can be None
• Ignoring Option wrapper for nullable fields
• Assuming Box is not allowed in structs

5. Given that arrays and linked lists store data linearly, which of the following real-world problems is best solved using a tree data structure instead?

medium

A. Storing a list of daily temperatures in order

B. Maintaining a queue of customers waiting in line

C. Storing a sequence of characters in a string

D. Representing a company's organizational chart with managers and employees

Solution

1. Step 1: Analyze each problem type

   Options A, B, and D represent linear data best suited for arrays or linked lists.

2. Step 2: Identify hierarchical data

   Representing a company's organizational chart with managers and employees describes an organizational chart, which is hierarchical and fits tree structures.

3. Final Answer:

   Representing a company's organizational chart with managers and employees -> Option D

4. Quick Check:

   Hierarchical data needs trees [OK]

Hint: Use trees for hierarchical data like org charts [OK]

Common Mistakes:

• Choosing linear data problems for trees
• Confusing queues or sequences with trees
• Ignoring data relationships