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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple array representing a list of fruits.

DSA Javascript

const fruits = ['apple', [1], 'banana'];
console.log(fruits);

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

A'potato'

B'carrot'

C'orange'

D'lettuce'

Attempts:

3 left

💡 Hint

Common Mistakes

Adding a vegetable instead of a fruit.

The array should contain fruit names. 'orange' fits correctly between 'apple' and 'banana'.

2fill in blank

medium

Complete the code to link nodes in a singly linked list.

DSA Javascript

function Node(value) {
  this.value = value;
  this.next = [1];
}

const first = new Node(1);
const second = new Node(2);
first.next = second;
console.log(first.next.value);

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

Anull

B0

Csecond

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined or a variable that is not yet defined.

When creating a new node, its next pointer should start as null to indicate the end of the list.

3fill in blank

hard

Fix the error in the tree node constructor to correctly assign children as an empty array.

DSA Javascript

function TreeNode(value) {
  this.value = value;
  this.children = [1];
}

const root = new TreeNode('root');
console.log(root.children.length);

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

Aundefined

B{}

Cnull

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using object literal {} instead of array [] for children.

Children should be an empty array to hold multiple child nodes in a tree structure.

4fill in blank

hard

Fill both blanks to create a linked list node and link it to the next node.

DSA Javascript

function ListNode(value) {
  this.value = value;
  this.next = [1];
}

const node1 = new ListNode(10);
const node2 = new ListNode(20);
node1.next = [2];
console.log(node1.next.value);

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

Anull

Bnode2

Cundefined

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to undefined or 0 instead of null.

Not linking node1 to node2 correctly.

When creating a new node, next is initially null. Then node1.next is set to node2 to link them.

5fill in blank

hard

Fill all three blanks to create a tree node, add a child, and print the child's value.

DSA Javascript

function TreeNode(value) {
  this.value = value;
  this.children = [1];
}

const parent = new TreeNode('parent');
const child = new TreeNode('child');
parent.children.[2](child);
console.log(parent.children[[3]].value);

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

A[]

Bpush

C0

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push.

Using wrong index to access child.

Children is an empty array. Use push to add the child. The first child's index is 0.

Practice

1. Which data structure is best suited to represent a family tree where each person can have multiple children?

easy

A. Stack

B. Array

C. Linked List

D. Tree

Solution

1. Step 1: Understand the hierarchy requirement

   A family tree has a parent-child relationship with multiple children per parent, which is a hierarchical structure.

2. Step 2: Match data structure to hierarchy

   Trees naturally represent hierarchical data with nodes and branches, allowing multiple children per node.

3. Final Answer:

   Tree -> Option D

4. Quick Check:

   Hierarchy with multiple children = Tree [OK]

Hint: Hierarchy with multiple children? Use Tree [OK]

Common Mistakes:

• Choosing Array which is linear, not hierarchical
• Choosing Linked List which supports only one next node
• Confusing Stack with hierarchical structure

2. Which of the following is the correct way to declare a linked list node in JavaScript?

easy

A. const node = { value: 5, next: null };

B. const node = [5, null];

C. const node = new Array(5, null);

D. const node = { next: 5, value: null };

Solution

1. Step 1: Understand linked list node structure

   A linked list node typically has a value and a pointer to the next node (next).

2. Step 2: Check each option for correct syntax

   const node = { value: 5, next: null }; correctly uses an object with 'value' and 'next' keys. Others either use arrays or swap keys incorrectly.

3. Final Answer:

   const node = { value: 5, next: null }; -> Option A

4. Quick Check:

   Linked list node = object with value and next [OK]

Hint: Linked list node = object with value and next [OK]

Common Mistakes:

• Using arrays instead of objects for nodes
• Swapping value and next keys
• Using Array constructor incorrectly

3. What will be the output of the following JavaScript code that builds a simple tree structure?

const tree = {
  value: 'root',
  children: [
    { value: 'child1', children: [] },
    { value: 'child2', children: [
      { value: 'grandchild1', children: [] }
    ] }
  ]
};

console.log(tree.children[1].children[0].value);

medium

A. "grandchild1"

B. "child2"

C. "child1"

D. undefined

Solution

1. Step 1: Trace the tree object structure

   The root has two children: 'child1' and 'child2'. 'child2' has one child: 'grandchild1'.

2. Step 2: Access the nested value

   tree.children[1] is 'child2', its children[0] is 'grandchild1', so accessing value gives 'grandchild1'.

3. Final Answer:

   "grandchild1" -> Option A

4. Quick Check:

   tree.children[1].children[0].value = "grandchild1" [OK]

Hint: Follow children indices step-by-step [OK]

Common Mistakes:

• Confusing child indices (0 vs 1)
• Assuming children is a single node, not array
• Accessing wrong property name

4. The following code attempts to create a linked list but has an error. What is the error?

const node1 = { value: 1, next: null };
const node2 = { value: 2, next: null };
node1.next = node2;
node2.next = node1;
console.log(node1.next.next.value);

medium

A. node2.next should be null, not node1

B. node1.next is null, so accessing next.next causes error

C. It creates an infinite loop by linking nodes circularly

D. Syntax error in object declaration

Solution

1. Step 1: Analyze the linked list connections

   node1.next points to node2, and node2.next points back to node1, creating a circular link.

2. Step 2: Understand the effect of circular links

   Accessing node1.next.next.value goes from node1 to node2, then back to node1, causing infinite traversal if looped.

3. Final Answer:

   It creates an infinite loop by linking nodes circularly -> Option C

4. Quick Check:

   Circular links cause infinite loops [OK]

Hint: Check if next points back to previous node [OK]

Common Mistakes:

• Ignoring circular reference causing infinite loop
• Assuming next.next is null
• Thinking it's a syntax error

5. You have a nested array representing a company's hierarchy like this:

const company = [
  { name: 'CEO', reports: [
    { name: 'Manager1', reports: [] },
    { name: 'Manager2', reports: [
      { name: 'Employee1', reports: [] }
    ] }
  ] }
];

Which data structure would be best to convert this into for efficient traversal and why?

hard

A. Convert to a Linked List because it allows easy sequential access to employees.

B. Convert to a Tree because it naturally represents hierarchical relationships with multiple children.

C. Convert to a flat Array because arrays are faster to traverse than trees.

D. Convert to a Stack because it helps in depth-first traversal.

Solution

1. Step 1: Understand the nested array structure

   The company hierarchy has multiple levels with managers and employees reporting to them, forming a hierarchy.

2. Step 2: Choose data structure matching hierarchy and traversal needs

   Trees represent hierarchical data with nodes and children, making traversal and queries efficient and natural.

3. Final Answer:

   Convert to a Tree because it naturally represents hierarchical relationships with multiple children. -> Option B

4. Quick Check:

   Hierarchical data = Tree for efficient traversal [OK]

Hint: Hierarchy with multiple levels? Use Tree [OK]

Common Mistakes:

• Choosing Linked List which is linear, not hierarchical
• Choosing flat Array losing hierarchy info
• Confusing Stack with data structure for storage