Trie Node Design and Initialization in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Trie Node Initialization

What is the output of the following TypeScript code that initializes a Trie node and prints its children keys?

DSA Typescript

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

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

const node = new TrieNode();
console.log(Array.from(node.children.keys()));

A [null]

B [undefined]

C []

D [" "]

💡 Hint

Think about what keys exist in a newly created empty Map.

A new TrieNode has an empty Map for children, so no keys exist. Converting keys to an array results in an empty array [].

❓ Predict Output

intermediate

Trie Node Children After Insert

After inserting a child node with key 'a' into a TrieNode's children Map, what is the output of printing the keys?

DSA Typescript

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

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

const node = new TrieNode();
node.children.set('a', new TrieNode());
console.log(Array.from(node.children.keys()));

A [undefined]

B ['a']

C ['A']

D []

💡 Hint

Check what key was added to the Map.

The key 'a' was added to the children Map, so printing keys shows ['a'].

🔧 Debug

advanced

Identify the Error in TrieNode Constructor

What error will this TypeScript code produce when creating a TrieNode instance?

DSA Typescript

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

  constructor() {
    this.children = {};
    this.children.set('a', new TrieNode());
    this.isEndOfWord = false;
  }
}

const node = new TrieNode();

A TypeError: this.children.set is not a function

B SyntaxError: Unexpected token {

C No error, code runs fine

D ReferenceError: TrieNode is not defined

💡 Hint

Check the type assigned to children and how Map methods are used.

Assigning {} to children means it's a plain object, not a Map. Calling Map methods like set on it causes TypeError.

🧠 Conceptual

advanced

Purpose of isEndOfWord in TrieNode

What is the main purpose of the isEndOfWord boolean property in a TrieNode?

A To mark if the node represents the end of a valid word

B To store the number of children nodes

C To keep track of the depth of the node in the Trie

D To hold the character value of the node

💡 Hint

Think about how a Trie distinguishes complete words from prefixes.

isEndOfWord marks nodes that complete a valid word, differentiating them from nodes that are just prefixes.

❓ Predict Output

expert

Final Trie Structure After Multiple Insertions

Given the following code inserting words into a Trie, what is the output of printing the root node's children keys?

DSA Typescript

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

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

class Trie {
  root: TrieNode;

  constructor() {
    this.root = new TrieNode();
  }

  insert(word: string) {
    let current = this.root;
    for (const char of word) {
      if (!current.children.has(char)) {
        current.children.set(char, new TrieNode());
      }
      current = current.children.get(char)!;
    }
    current.isEndOfWord = true;
  }
}

const trie = new Trie();
trie.insert('cat');
trie.insert('car');
trie.insert('dog');
console.log(Array.from(trie.root.children.keys()));

A ['cat', 'car', 'dog']

B ['a', 'o']

C []

D ['c', 'd']

💡 Hint

The root's children keys are the first letters of inserted words.

Words 'cat' and 'car' start with 'c', 'dog' starts with 'd', so root children keys are ['c', 'd'].