Word Search in Trie in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Trie node with an empty children map.

DSA Typescript

class TrieNode {
  children: Map<string, TrieNode> = new Map();
  isEndOfWord: boolean = false;
}

const node = new TrieNode();
node.children.[1]('a', new TrieNode());

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

Ainsert

Badd

Cpush

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' or 'push' which are not methods of Map.

Trying to assign directly without using a method.

The Map object uses the 'set' method to add key-value pairs. Here, 'a' is the key and a new TrieNode is the value.

2fill in blank

medium

Complete the code to check if a character exists in the children map of a Trie node.

DSA Typescript

function hasChild(node: TrieNode, char: string): boolean {
  return node.children.[1](char);
}

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

Ahas

Bcontains

Cincludes

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'contains' or 'includes' which are not Map methods.

Trying to access children[char] directly without checking.

The Map object has a 'has' method to check if a key exists.

3fill in blank

hard

Fix the error in the insert method to correctly add characters to the Trie.

DSA Typescript

class Trie {
  root: TrieNode = new TrieNode();

  insert(word: string): void {
    let current = this.root;
    for (const char of word) {
      if (!current.children.[1](char)) {
        current.children.set(char, new TrieNode());
      }
      current = current.children.get(char)!;
    }
    current.isEndOfWord = true;
  }
}

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

Aset

Bget

Chas

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'get' which returns a value, not a boolean.

Using 'set' which adds or updates a value, not checks existence.

We need to check if the children map has the character key before adding a new node. The 'has' method is used for this check.

4fill in blank

hard

Fill both blanks to complete the search method that returns true if the word exists in the Trie.

DSA Typescript

class Trie {
  root: TrieNode = new TrieNode();

  search(word: string): boolean {
    let current = this.root;
    for (const char of word) {
      if (!current.children.[1](char)) {
        return false;
      }
      current = current.children.[2](char)!;
    }
    return current.isEndOfWord;
  }
}

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

Ahas

Bget

Cset

Dcontains

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'set' instead of 'get' to retrieve a node.

Using 'contains' which is not a Map method.

To check if a character exists, use 'has'. To get the child node, use 'get'.

5fill in blank

hard

Fill all three blanks to complete the method that checks if any word in the Trie starts with the given prefix.

DSA Typescript

class Trie {
  root: TrieNode = new TrieNode();

  startsWith(prefix: string): boolean {
    let current = this.root;
    for (const char of prefix) {
      if (!current.children.[1](char)) {
        return false;
      }
      current = current.children.[2](char)!;
    }
    return [3];
  }
}

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

Ahas

Bget

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Returning false at the end instead of true.

Using 'set' instead of 'get' to retrieve nodes.

We check if each character exists with 'has', get the node with 'get', and if all characters are found, return true.

Practice

1. What is the main purpose of using a Trie data structure in word search problems?

easy

A. To efficiently store and search words by their prefixes

B. To sort words alphabetically

C. To store words in a linked list format

D. To perform arithmetic operations on words

Solution

1. Step 1: Understand the Trie structure

   A Trie stores characters in a tree where each path represents a prefix of words.

2. Step 2: Identify the use in word search

   This structure allows quick prefix-based search, making it efficient for word search problems.

3. Final Answer:

   To efficiently store and search words by their prefixes -> Option A

4. Quick Check:

   Trie = prefix search [OK]

Hint: Trie is all about prefixes and fast word lookup [OK]

Common Mistakes:

• Confusing Trie with sorting structures
• Thinking Trie stores words linearly
• Assuming Trie performs arithmetic

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

easy

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

B. class TrieNode { children: string[]; isEndOfWord: number; constructor() { this.children = []; this.isEndOfWord = 0; } }

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

D. class TrieNode { children: object; isEndOfWord: string; constructor() { this.children = {}; this.isEndOfWord = 'false'; } }

Solution

1. Step 1: Check children type

   Children should be a Map from string to TrieNode for efficient character mapping.

2. Step 2: Check isEndOfWord type and initialization

   It should be a boolean initialized to false to mark word endings correctly.

3. Final Answer:

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

4. Quick Check:

   Correct types and initialization [OK]

Hint: Use Map and boolean for end flag [OK]

Common Mistakes:

• Using array instead of Map for children
• Using wrong types for isEndOfWord
• Initializing isEndOfWord incorrectly

3. Given the following TypeScript code snippet for searching a word in a Trie, what will be the output when searching for the word "cat" if only "car" and "cap" are inserted?

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

class Trie {
  root = new TrieNode();

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

  search(word: string): boolean {
    let node = this.root;
    for (const ch of word) {
      if (!node.children.has(ch)) return false;
      node = node.children.get(ch)!;
    }
    return node.isEndOfWord;
  }
}

const trie = new Trie();
trie.insert("car");
trie.insert("cap");
console.log(trie.search("cat"));

medium

A. true

B. false

C. undefined

D. Runtime error

Solution

1. Step 1: Trace insertion of "car" and "cap"

   Both words create nodes for 'c', 'a', then diverge at 'r' and 'p' respectively, marking those ends as true.

2. Step 2: Trace search for "cat"

   Search finds 'c' and 'a', but 't' is not a child of 'a', so search returns false.

3. Final Answer:

   false -> Option B

4. Quick Check:

   Word not inserted = false [OK]

Hint: If last char missing, search returns false [OK]

Common Mistakes:

• Assuming partial prefix means true
• Confusing isEndOfWord with node existence
• Expecting undefined instead of false

4. Identify the bug in the following TypeScript Trie search method that causes it to always return false:

search(word: string): boolean {
  let node = this.root;
  for (const ch of word) {
    if (!node.children.has(ch)) return false;
    node = node.children.get(ch)!;
  }
  return node.isEndOfWord === false;
}

medium

A. The method should return true before the loop ends

B. The loop should iterate backwards over the word

C. The children map should be an array instead

D. The return condition should be node.isEndOfWord, not its negation

Solution

1. Step 1: Analyze the return statement

   The method returns node.isEndOfWord === false, which means it returns true if the word is NOT ending here.

2. Step 2: Correct the return logic

   It should return node.isEndOfWord to confirm the word ends at this node.

3. Final Answer:

   The return condition should be node.isEndOfWord, not its negation -> Option D

4. Quick Check:

   Return true if word ends here [OK]

Hint: Return node.isEndOfWord directly to confirm word end [OK]

Common Mistakes:

• Returning negation of isEndOfWord
• Changing loop direction unnecessarily
• Using wrong data structure for children

5. You want to implement a function that finds all words in a Trie starting with a given prefix. Which approach correctly combines Trie traversal and backtracking to collect all matching words?

hard

A. Search each word in the Trie individually to check prefix match

B. Store all words in an array and filter by prefix each time

C. Traverse Trie nodes for prefix, then recursively collect words from that node using backtracking

D. Use a hash map to map prefixes to words without Trie traversal

Solution

1. Step 1: Traverse Trie to prefix node

   Follow characters of prefix to reach the node representing last prefix character.

2. Step 2: Use backtracking from prefix node

   Recursively explore all children nodes to collect complete words starting with prefix.

3. Final Answer:

   Traverse Trie nodes for prefix, then recursively collect words from that node using backtracking -> Option C

4. Quick Check:

   Prefix traversal + backtracking = Traverse Trie nodes for prefix, then recursively collect words from that node using backtracking [OK]

Hint: Find prefix node, then backtrack to collect words [OK]

Common Mistakes:

• Checking all words instead of prefix traversal
• Filtering array instead of Trie traversal
• Using hash map without Trie structure