Word Search in Trie in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Javascript

function createNode() {
  return { children: [1] };
}

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

Anull

B[]

C{}

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using an array [] instead of an object for children.

The children of a Trie node should be an empty object to hold child nodes by character keys.

2fill in blank

medium

Complete the code to check if a character exists in the current Trie node's children.

DSA Javascript

if (node.children.hasOwnProperty([1])) {
  // character exists
}

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

Achar

B'char'

Cnode

Dchildren

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string literal 'char' instead of the variable char.

We check if the children object has the key named by the variable char.

3fill in blank

hard

Fix the error in the search function to return true if the word is found in the Trie.

DSA Javascript

function search(word) {
  let node = root;
  for (let char of word) {
    if (!node.children.hasOwnProperty(char)) {
      return false;
    }
    node = node.children[[1]];
  }
  return node.isEnd === true;
}

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

Aword

Bchar

Cnode

Dchildren

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'word' or 'node' instead of 'char' as the key.

We must use the current character variable 'char' to move to the next node.

4fill in blank

hard

Fill both blanks to insert a word into the Trie correctly.

DSA Javascript

function insert(word) {
  let node = root;
  for (let char of word) {
    if (!node.children.hasOwnProperty([1])) {
      node.children[[2]] = createNode();
    }
    node = node.children[char];
  }
  node.isEnd = true;
}

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

Achar

Bword

Cnode

Dchildren

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables like 'word' or 'node' instead of 'char'.

We check and add the child node using the current character 'char' in both blanks.

5fill in blank

hard

Fill all three blanks to create a function that searches for a prefix in the Trie.

DSA Javascript

function startsWith(prefix) {
  let node = root;
  for (let [1] of prefix) {
    if (!node.children.hasOwnProperty([2])) {
      return false;
    }
    node = node.children[[3]];
  }
  return true;
}

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

Achar

Bprefix

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prefix' or 'node' instead of 'char' for keys.

The loop variable is 'char', and we use 'char' to check and move through children.

Practice

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

easy

A. To efficiently store and search words by their prefixes

B. To sort words alphabetically

C. To store words in a hash table

D. To perform arithmetic operations on words

Solution

1. Step 1: Understand Trie structure

   A Trie stores characters of words in a tree where each node represents a character.

2. Step 2: Identify Trie usage

   It allows quick prefix-based search by traversing nodes matching characters.

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 prefix-based fast word search [OK]

Common Mistakes:

• Confusing Trie with hash tables
• Thinking Trie sorts words
• Assuming Trie does arithmetic

2. Which of the following is the correct way to check if a word exists in a Trie in JavaScript?

easy

A. Use a loop to traverse nodes matching each character and check end flag

B. Use Array.includes(word) on the Trie object

C. Use JSON.stringify on Trie and search substring

D. Use Math.max on character codes of the word

Solution

1. Step 1: Understand Trie search method

   Search involves traversing nodes for each character and checking if the word ends at last node.

2. Step 2: Eliminate incorrect options

   Array.includes and JSON.stringify are not suitable for Trie structure. Math.max is unrelated.

3. Final Answer:

   Use a loop to traverse nodes matching each character and check end flag -> Option A

4. Quick Check:

   Traverse nodes + check end = correct search [OK]

Hint: Traverse each character node and check end flag [OK]

Common Mistakes:

• Using array methods on Trie
• Trying to convert Trie to string
• Applying math functions on words

3. What will be the output of the following code snippet?

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

class Trie {
  constructor() {
    this.root = new TrieNode();
  }
  insert(word) {
    let node = this.root;
    for (const char of word) {
      if (!node.children[char]) node.children[char] = new TrieNode();
      node = node.children[char];
    }
    node.isEnd = true;
  }
  search(word) {
    let node = this.root;
    for (const char of word) {
      if (!node.children[char]) return false;
      node = node.children[char];
    }
    return node.isEnd;
  }
}

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

medium

A. false false

B. false true

C. true false

D. true true

Solution

1. Step 1: Insert words 'cat' and 'car'

   Both words are added character by character, marking end nodes for 't' and 'r'.

2. Step 2: Search 'cat' and 'cap'

   'cat' exists with isEnd true, 'cap' path breaks at 'p' missing node, returns false.

3. Final Answer:

   true false -> Option C

4. Quick Check:

   Search 'cat' = true, 'cap' = false [OK]

Hint: Check inserted words and search path carefully [OK]

Common Mistakes:

• Assuming 'cap' exists after inserting 'car'
• Confusing isEnd flag
• Ignoring missing child nodes

4. Identify the bug in the following Trie search method and select the fix:

search(word) {
  let node = this.root;
  for (const char of word) {
    if (!node.children[char]) return false;
    node = node.children[char];
  }
  return true;
}

medium

A. Return false at the end instead of true

B. Add a check for empty word before loop

C. Change for loop to while loop

D. Return node.isEnd instead of true to confirm full word match

Solution

1. Step 1: Analyze current search return

   Returns true if path exists but does not check if word ends here.

2. Step 2: Correct return value

   Must return node.isEnd to confirm the word is complete, not just prefix.

3. Final Answer:

   Return node.isEnd instead of true to confirm full word match -> Option D

4. Quick Check:

   Check isEnd flag to confirm word end [OK]

Hint: Always check isEnd flag to confirm full word [OK]

Common Mistakes:

• Returning true without checking isEnd
• Changing loop type unnecessarily
• Ignoring empty word cases

5. Given a list of words, how can you use a Trie to find all words that start with a given prefix efficiently? Choose the best approach.

hard

A. Sort words and use binary search on prefix

B. Insert all words into Trie, traverse prefix nodes, then collect all descendant words

C. Use a hash map with prefix keys for direct lookup

D. Check each word in list if it starts with prefix using string methods

Solution

1. Step 1: Insert all words into Trie

   Build Trie so each word is represented by a path of nodes.

2. Step 2: Traverse prefix nodes and collect words

   Find node matching prefix end, then recursively collect all words below it.

3. Step 3: Compare other options

   Sorting and binary search is possible but less efficient for many queries. Hash maps need many keys. Checking each word is slow.

4. Final Answer:

   Insert all words into Trie, traverse prefix nodes, then collect all descendant words -> Option B

5. Quick Check:

   Trie + prefix traversal = efficient prefix search [OK]

Hint: Use Trie prefix traversal then gather descendant words [OK]

Common Mistakes:

• Ignoring Trie traversal for prefix
• Using slow linear search for prefix
• Confusing hash map with Trie