Trie Node Design and Initialization in DSA Typescript - Execution Trace

Concept Flow - Trie Node Design and Initialization

Create TrieNode class

↓

Initialize children map/dictionary

↓

Set isEndOfWord flag to false

↓

Ready to use node in Trie structure

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

Execution Sample

DSA Typescript

class TrieNode {
  children: Map<string, TrieNode>;
  isEndOfWord: boolean;

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

Defines a TrieNode class with a map for children nodes and a boolean flag to mark the end of a word.

Execution Table

Step	Operation	Children Map State	isEndOfWord	Visual State
1	Create new TrieNode instance	{}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }
2	Initialize children as empty Map	{}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }
3	Set isEndOfWord to false	{}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }
4	Node ready for insertion in Trie	{}	false	TrieNode { children: Map(0) {}, isEndOfWord: false }

💡 Initialization complete; node is empty with no children and not marking end of word.

Variable Tracker

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

Key Moments - 3 Insights

Why is children initialized as an empty Map instead of an array or object?

Using a Map allows efficient insertion and lookup of child nodes by character keys, as shown in execution_table step 2 where children is set to an empty Map {}.

Why is isEndOfWord set to false initially?

Because when a node is created, it does not yet represent the end of any word. This is confirmed in execution_table step 3 where isEndOfWord is set to false.

What does the visual state represent after initialization?

It shows the node has no children and does not mark the end of a word, matching the empty children map and false flag in execution_table rows.

Visual Quiz - 3 Questions

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

A undefined

B {} (empty Map)

C null

D Array with one element

💡 Hint

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

At which step is isEndOfWord set to false?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'isEndOfWord' column in execution_table to find when it changes.

If we did not initialize children as an empty Map, what would happen when inserting a child node?

A Insertion would fail because children is undefined

B Insertion would work normally

C isEndOfWord would become true automatically

D The node would delete itself

💡 Hint

Refer to variable_tracker for children variable state before initialization.

Concept Snapshot

TrieNode Design:
- children: Map<string, TrieNode> to hold child nodes
- isEndOfWord: boolean flag for word end
- Initialize children as empty Map
- Set isEndOfWord to false
- Ready for Trie insertion

Full Transcript

We create a TrieNode class with two main parts: a children map to hold links to next nodes, and a boolean flag isEndOfWord to mark if the node ends a word. Initially, children is empty and isEndOfWord is false. This setup allows us to build a Trie by adding child nodes for each character and marking word ends. The execution table shows each step of initialization, confirming the node starts empty and not marking any word end. This design supports efficient Trie operations like insert and search.

Practice

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

easy

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

B. To store integer values for sorting

C. To hold a single string value only

D. To act as a queue for BFS traversal

Solution

1. Step 1: Understand Trie node role

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

2. Step 2: Eliminate incorrect options

   The remaining options do not describe the Trie node's role correctly.

3. Final Answer:

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

4. Quick Check:

   Trie node = character + child links [OK]

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

Common Mistakes:

• Thinking Trie nodes store full words
• Confusing Trie nodes with arrays or queues
• Assuming Trie nodes store integer values

2. Which of the following is the correct TypeScript syntax to declare a Trie node class with a children map and an endOfWord boolean?

easy

A. class TrieNode { children: Map; endOfWord: boolean; constructor() { this.children = new Map(); this.endOfWord = true; } }

B. class TrieNode { children: Map; endOfWord: boolean; constructor() { this.children = new Map(); this.endOfWord = false; } }

C. class TrieNode { children: string[]; endOfWord: string; constructor() { this.children = []; this.endOfWord = ''; } }

D. class TrieNode { children: Map; endOfWord: boolean; constructor() { this.children = new Map(); this.endOfWord = false; } }

Solution

1. Step 1: Check children type

   Children should be a Map from string to TrieNode, not string[] or Map.

2. Step 2: Check endOfWord type and initialization

   endOfWord should be boolean, initialized to false.

3. Final Answer:

   class TrieNode { children: Map; endOfWord: boolean; constructor() { this.children = new Map(); this.endOfWord = false; } } -> Option B

4. Quick Check:

   Children: Map<string, TrieNode> + boolean endOfWord=false [OK]

Hint: Children map keys are characters (string), values are TrieNodes [OK]

Common Mistakes:

• Using array instead of Map for children
• Using wrong types for endOfWord
• Initializing endOfWord to true by default

3. Given the following TypeScript TrieNode class and code snippet, what will be the output of console.log(root.children.has('a')) after execution?

class TrieNode {
  children: Map;
  endOfWord: boolean;
  constructor() {
    this.children = new Map();
    this.endOfWord = false;
  }
}

const root = new TrieNode();
root.children.set('a', new TrieNode());

medium

A. undefined

B. false

C. true

D. Error

Solution

1. Step 1: Understand children map after insertion

   We add a key 'a' with a new TrieNode as value to root.children map.

2. Step 2: Check if 'a' key exists

   Calling root.children.has('a') returns true because 'a' was added.

3. Final Answer:

   true -> Option C

4. Quick Check:

   Map has key 'a' = true [OK]

Hint: Map.has(key) returns true if key was set before [OK]

Common Mistakes:

• Assuming has returns the value instead of boolean
• Confusing undefined with false
• Expecting error due to missing key

4. Identify the error in the following TypeScript TrieNode class code snippet:

class TrieNode {
  children: Map;
  endOfWord: boolean;
  constructor() {
    this.children = new Map();
    this.endOfWord = 'false';
  }
}

medium

A. endOfWord is assigned a string instead of boolean

B. children map is not initialized

C. Missing semicolon after constructor

D. Map keys should be number, not string

Solution

1. Step 1: Check endOfWord type and assignment

   endOfWord is declared boolean but assigned string 'false', causing type error.

2. Step 2: Verify children initialization and syntax

   children map is correctly initialized; semicolons are optional in TypeScript; keys as string are correct.

3. Final Answer:

   endOfWord is assigned a string instead of boolean -> Option A

4. Quick Check:

   Boolean variable assigned string = error [OK]

Hint: Boolean variables must be true or false, not strings [OK]

Common Mistakes:

• Assigning 'false' (string) instead of false (boolean)
• Thinking Map keys must be numbers
• Confusing missing semicolons as errors

5. You want to design a TrieNode class in TypeScript that supports Unicode characters as keys and efficiently checks if a node marks the end of a word. Which of the following is the best design choice?

hard

A. Use a Set<string> for children and a boolean endOfWord initialized to true

B. Use an object with fixed keys for children and a string endOfWord to store word

C. Use an array of TrieNode for children indexed by character code and endOfWord as number

D. Use a Map for children and a boolean endOfWord initialized to false

Solution

1. Step 1: Consider Unicode support for children keys

   Map supports any string keys including Unicode characters efficiently.

2. Step 2: Check endOfWord type for marking word end

   Boolean endOfWord initialized to false is standard to mark if node ends a word.

3. Step 3: Evaluate other options

   Objects with fixed keys limit flexibility; arrays indexed by char code waste space; Set<string> cannot map to child nodes.

4. Final Answer:

   Use a Map for children and a boolean endOfWord initialized to false -> Option D

5. Quick Check:

   Unicode keys + boolean flag = Use a Map for children and a boolean endOfWord initialized to false [OK]

Hint: Map handles Unicode keys best [OK]

Common Mistakes:

• Using arrays limits Unicode support
• Using Set for children loses child node mapping
• Using string instead of boolean for endOfWord