Trie Search Operation in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of the Trie search for 'cat'?

Given the following Trie implementation and insertions, what will be the output of searching for the word 'cat'?

DSA Javascript

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

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

const trie = new Trie();
trie.insert('cat');
trie.insert('car');
trie.insert('dog');

console.log(trie.search('cat'));

A true

B TypeError

C undefined

D false

💡 Hint

Check if the search method returns true only when the word is fully present and marked as end of word.

The word 'cat' was inserted into the Trie and marked as an end of a word. The search method returns true when the full word is found and the last node is marked as end of word.

❓ Predict Output

intermediate

What is the output of searching for 'ca' in the Trie?

Using the same Trie from the previous example, what will be the output of searching for the word 'ca'?

DSA Javascript

console.log(trie.search('ca'));

A true

B false

C undefined

D TypeError

💡 Hint

Remember that 'ca' is a prefix but not a complete word inserted.

The search method returns false because 'ca' is only a prefix in the Trie, not marked as an end of a word.

🧠 Conceptual

advanced

Which statement about Trie search operation is correct?

Choose the correct statement about how the search operation works in a Trie data structure.

A Search returns true if all characters of the word are found in sequence and the last node is marked as end of word.

B Search returns true if the word is a prefix of any inserted word, regardless of end of word marking.

C Search returns true if the first character of the word is found in the Trie root children.

D Search returns true only if the word length is greater than 5 characters.

💡 Hint

Think about what makes a word complete in a Trie.

A Trie search returns true only if the entire word is found character by character and the last character node is marked as the end of a word.

🔧 Debug

advanced

What error occurs when searching for a word with a missing character node?

Consider the Trie search method. What happens if the search word contains a character not present in the Trie nodes?

DSA Javascript

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

A Returns undefined

B Throws a ReferenceError

C Returns false indicating word not found

D Throws a TypeError

💡 Hint

Check the condition when a character node is missing.

The search method returns false immediately when a character node is missing, indicating the word is not present.

🚀 Application

expert

How many words are found after inserting and searching in the Trie?

After inserting the words ['apple', 'app', 'application', 'bat', 'bath'] into an empty Trie, how many of these words will return true when searched?

DSA Javascript

const trie = new Trie();
['apple', 'app', 'application', 'bat', 'bath'].forEach(word => trie.insert(word));

const results = ['apple', 'app', 'application', 'bat', 'bath'].map(word => trie.search(word));
const count = results.filter(Boolean).length;
console.log(count);

A 4

B 2

C 3

D 5

💡 Hint

All inserted words are marked as end of word nodes.

All inserted words are present and marked as complete words, so all searches return true, count is 5.

Practice

1. What does the search operation in a Trie data structure primarily check for?

easy

A. The length of the longest word in the Trie

B. If the Trie is empty

C. If a given word exists in the Trie

D. The number of words stored in the Trie

Solution

1. Step 1: Understand the purpose of Trie search

   The search operation in a Trie is designed to check if a specific word is present in the Trie by traversing nodes corresponding to each character.

2. Step 2: Identify what the search confirms

   It confirms the presence or absence of the entire word, not the count or length of words stored.

3. Final Answer:

   If a given word exists in the Trie -> Option C

4. Quick Check:

   Trie search checks word existence [OK]

Hint: Search checks full word presence in Trie nodes [OK]

Common Mistakes:

• Confusing search with counting words
• Thinking search returns word length
• Assuming search checks if Trie is empty

2. Which of the following is the correct way to check if a character node exists in a Trie during search in JavaScript?

easy

A. if (node.char !== null)

B. if (node[char] !== undefined)

C. if (node.has(char))

D. if (node.char === true)

Solution

1. Step 1: Understand Trie node structure in JavaScript

   Trie nodes are usually objects where keys are characters. Checking if a character exists uses property access and undefined check.

2. Step 2: Identify correct syntax for existence check

   Using node[char] !== undefined correctly checks if the character key exists in the node object.

3. Final Answer:

   if (node[char] !== undefined) -> Option B

4. Quick Check:

   Check node property with !== undefined [OK]

Hint: Use node[char] !== undefined to check character node [OK]

Common Mistakes:

• Using dot notation with variable char
• Using incorrect method like has() on object
• Checking for null instead of undefined

3. What will be the output of the following JavaScript 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. true false

B. false true

C. true true

D. false false

Solution

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

   Both words are inserted by creating nodes for each character and marking the last node's isEnd as true.

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

   'cat' exists fully with isEnd true, so search returns true. 'cap' is missing 'p' node, so search returns false.

3. Final Answer:

   true false -> Option A

4. Quick Check:

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

Hint: Search returns true only if full word and isEnd true [OK]

Common Mistakes:

• Assuming partial matches return true
• Not setting isEnd flag on insert
• Confusing children object access

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

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

medium

A. Use 'for (let i=0; i

B. Change '===' to '!==' in the if condition

C. Initialize node with a new TrieNode inside the method

D. Return node.isEnd instead of true at the end

Solution

1. Step 1: Analyze the search method's return value

   The method returns true after traversing all characters without checking if the last node marks the end of a word.

2. Step 2: Correct the return to check word completion

   Return node.isEnd to confirm the word ends here, not just prefix exists.

3. Final Answer:

   Return node.isEnd instead of true at the end -> Option D

4. Quick Check:

   Check isEnd flag to confirm full word [OK]

Hint: Always check isEnd flag after traversal [OK]

Common Mistakes:

• Returning true without isEnd check
• Changing comparison operator incorrectly
• Unnecessary loop syntax changes

5. Given a Trie containing the words ['apple', 'app', 'bat', 'bath'], which of the following search queries will return true? Assume the search method correctly checks for full word presence. Select the correct combination.

hard

A. search('app'), search('bat'), search('bath')

B. search('appl'), search('bat'), search('bath')

C. search('apple'), search('bat'), search('batman')

D. search('app'), search('bath'), search('batman')

Solution

1. Step 1: Identify words present in the Trie

   The Trie contains 'apple', 'app', 'bat', and 'bath'. Only these exact words return true on search.

2. Step 2: Check each option's search queries

   search('app'), search('bat'), search('bath') searches 'app', 'bat', 'bath' all present. Others include partial or missing words like 'appl' or 'batman' which return false.

3. Final Answer:

   search('app'), search('bat'), search('bath') -> Option A

4. Quick Check:

   Only full words in Trie return true [OK]

Hint: Search true only for full words inserted in Trie [OK]

Common Mistakes:

• Assuming partial words return true
• Confusing prefixes with full words
• Including words not inserted in Trie