Trie Node Design and Initialization in DSA Javascript - Execution Trace

Concept Flow - Trie Node Design and Initialization

Create new TrieNode object

↓

Initialize children map (empty)

↓

Set isEndOfWord flag to false

↓

TrieNode ready for insertion or traversal

This flow shows how a Trie node is created with an empty children map and a flag to mark word endings.

Execution Sample

DSA Javascript

class TrieNode {
  constructor() {
    this.children = new Map();
    this.isEndOfWord = false;
  }
}

This code defines a Trie node with a map for children and a boolean flag for word end.

Execution Table

Step	Operation	Children Map State	isEndOfWord Flag	Visual State
1	Create new TrieNode object	{}	false	TrieNode {}
2	Initialize children as empty Map	Map(0) {}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }
3	Set isEndOfWord to false	Map(0) {}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }
4	TrieNode ready for use	Map(0) {}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }

💡 Initialization complete; node ready for insertion or traversal.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
children	undefined	undefined	Map(0) {}	Map(0) {}	Map(0) {}
isEndOfWord	undefined	undefined	undefined	false	false

Key Moments - 3 Insights

Why do we use a Map for children instead of an object or array?

Using a Map allows flexible keys (characters) and efficient lookups. The execution_table step 2 shows children initialized as an empty Map, ready to store any character keys.

Why is isEndOfWord initialized to false?

Because when a node is created, it does not represent the end of a word yet. Step 3 in the execution_table sets isEndOfWord to false to mark this initial state.

What does the empty children Map mean for the TrieNode?

It means the node has no children yet, so no paths to other characters. This is shown in the visual state in all steps where children is Map(0) {}.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the state of the children map?

A A Map with one entry

B An empty Map with zero entries

C Undefined

D An array of characters

💡 Hint

Check the 'Children Map State' column at step 2 in the execution_table.

At which step is the isEndOfWord flag set to false?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'isEndOfWord Flag' column in the execution_table.

If we did not initialize children as a Map, what would happen to the TrieNode?

A It would be ready for insertion

B It would automatically create children

C It would have no way to store child nodes

D It would mark end of word

💡 Hint

Refer to the variable_tracker for 'children' variable initialization.

Concept Snapshot

TrieNode Design:
- children: Map to store child nodes by character
- isEndOfWord: boolean flag for word end
Initialization:
- children = new Map()
- isEndOfWord = false
Ready for insertion/traversal

Full Transcript

This visualization shows how a TrieNode is created and initialized. First, a new TrieNode object is created. Then, its children property is set to an empty Map to hold child nodes. Next, the isEndOfWord flag is set to false because the node does not represent the end of a word yet. After these steps, the TrieNode is ready to be used in a Trie for inserting or searching words. The execution table tracks these steps with the state of children and isEndOfWord. The variable tracker shows how children and isEndOfWord change from undefined to their initialized values. Common confusions include why a Map is used for children and why isEndOfWord starts as false. The quiz questions check understanding of these states at different steps.

Practice

1. What is the main purpose of a Trie node in a Trie data structure?

easy

A. To store the entire word in one node

B. To store integer values for sorting

C. To hold only the last character of a word

D. To store characters and links to child nodes representing prefixes

Solution

1. Step 1: Understand Trie node role

   A Trie node stores a character and links to child nodes that represent possible next characters in words.

2. Step 2: Compare options

   Only To store characters and links to child nodes representing prefixes correctly describes storing characters and child links for prefixes.

3. Final Answer:

   To store characters and links to child nodes representing prefixes -> Option D

4. Quick Check:

   Trie node = character + child links [OK]

Hint: Trie nodes hold characters and children, not full words [OK]

Common Mistakes:

• Thinking nodes store whole words
• Confusing Trie nodes with array elements
• Assuming nodes only store last characters

2. Which of the following is the correct way to initialize a Trie node in JavaScript with an empty children object and a boolean flag isEndOfWord set to false?

easy

A. const node = { children: null, isEndOfWord: true };

B. const node = { children: [], isEndOfWord: false };

C. const node = { children: {}, isEndOfWord: false };

D. const node = { children: {}, isEndOfWord: true };

Solution

1. Step 1: Identify correct children type

   Children should be an object to map characters to nodes, so {} is correct.

2. Step 2: Check isEndOfWord initial value

   Initially, isEndOfWord should be false because the node does not end a word yet.

3. Final Answer:

   const node = { children: {}, isEndOfWord: false }; -> Option C

4. Quick Check:

   Empty object + false flag = correct initialization [OK]

Hint: Children is an object, isEndOfWord starts false [OK]

Common Mistakes:

• Using array instead of object for children
• Setting isEndOfWord true at initialization
• Setting children to null

3. Consider this JavaScript code snippet for a Trie node:

class TrieNode {
  constructor() {
    this.children = {};
    this.isEndOfWord = false;
  }
}

const node = new TrieNode();
console.log(node.isEndOfWord);
console.log(Object.keys(node.children).length);

What will be the output?

medium

A. false
0

B. true
0

C. false
undefined

D. undefined
0

Solution

1. Step 1: Check isEndOfWord value after construction

   Constructor sets isEndOfWord to false, so console.log prints false.

2. Step 2: Check children keys count

   Children is an empty object, so Object.keys(node.children).length is 0.

3. Final Answer:

   false 0 -> Option A

4. Quick Check:

   isEndOfWord = false, children keys = 0 [OK]

Hint: Empty children means zero keys; isEndOfWord defaults false [OK]

Common Mistakes:

• Assuming isEndOfWord is true by default
• Expecting children keys length to be undefined
• Confusing object keys count with children length

4. The following code attempts to create a Trie node but has an error:

function TrieNode() {
  this.children = [];
  this.isEndOfWord = false;
}

What is the main problem with this code?

medium

A. children should be an object, not an array

B. isEndOfWord should be true initially

C. Function should return a value

D. Missing semicolon after isEndOfWord assignment

Solution

1. Step 1: Analyze children data type

   Children must be an object to map characters to nodes, not an array.

2. Step 2: Check other parts

   isEndOfWord false is correct; function constructors do not need explicit return; semicolons are optional in JS.

3. Final Answer:

   children should be an object, not an array -> Option A

4. Quick Check:

   Children = object, not array [OK]

Hint: Children must be object for character keys, not array [OK]

Common Mistakes:

• Thinking arrays can map characters
• Expecting function constructors to return explicitly
• Focusing on semicolon errors

5. You want to design a Trie node class in JavaScript that supports Unicode characters as keys in children and initializes isEndOfWord to false. Which of the following implementations correctly achieves this and allows adding child nodes dynamically?

hard

A. class TrieNode {
constructor() {
this.children = {};
this.isEndOfWord = true;
}
addChild(char) {
this.children[char] = new TrieNode();
}
}

B. class TrieNode {
constructor() {
this.children = new Map();
this.isEndOfWord = false;
}
addChild(char) {
if (!this.children.has(char)) {
this.children.set(char, new TrieNode());
}
}
}

C. class TrieNode {
constructor() {
this.children = [];
this.isEndOfWord = false;
}
addChild(char) {
this.children.push(char);
}
}

D. class TrieNode {
constructor() {
this.children = new Set();
this.isEndOfWord = false;
}
addChild(char) {
this.children.add(char);
}
}

Solution

1. Step 1: Check children data structure for Unicode support

   Using Map allows any string keys including Unicode, better than plain objects.

2. Step 2: Verify isEndOfWord initialization and addChild method

   isEndOfWord is false initially, and addChild adds new TrieNode only if missing, correctly updating children Map.

3. Step 3: Compare other options

   class TrieNode { constructor() { this.children = {}; this.isEndOfWord = true; } addChild(char) { this.children[char] = new TrieNode(); } } sets isEndOfWord true initially (wrong). class TrieNode { constructor() { this.children = []; this.isEndOfWord = false; } addChild(char) { this.children.push(char); } } uses array which can't map chars to nodes. class TrieNode { constructor() { this.children = new Set(); this.isEndOfWord = false; } addChild(char) { this.children.add(char); } } uses Set which stores chars but not nodes.

4. Final Answer:

   Implementation using Map with isEndOfWord false and addChild method -> Option B

5. Quick Check:

   Map + false flag + dynamic addChild = correct Trie node [OK]

Hint: Use Map for Unicode keys and false isEndOfWord [OK]

Common Mistakes:

• Using array or Set instead of Map or object
• Setting isEndOfWord true at start
• Not checking if child exists before adding