Trie Search Operation in DSA Typescript - Build from Scratch

Trie Search Operation

📖 Scenario: You are building a simple word search tool for a small dictionary. The tool uses a Trie data structure to store words and quickly check if a word exists.

🎯 Goal: Build a Trie with given words and implement a search operation to check if a word is present in the Trie.

📋 What You'll Learn

Create a TrieNode class with a children map and an isEndOfWord boolean

Create a Trie class with insert and search methods

Insert given words into the Trie

Search for a given word in the Trie and return true if found, false otherwise

💡 Why This Matters

🌍 Real World

Tries are used in autocomplete systems, spell checkers, and IP routing to quickly find words or prefixes.

💼 Career

Understanding Trie search operations is important for roles involving text processing, search engines, and efficient data retrieval.

1

Create TrieNode and Trie classes with insert method

Create a class called TrieNode with a property children as a Map from string to TrieNode and a boolean property isEndOfWord initialized to false. Then create a class called Trie with a property root initialized as a new TrieNode. Add an insert method to Trie that takes a word string and inserts it into the Trie.

DSA Typescript

// Define TrieNode and Trie classes with insert method
// Your code here

Hint

Use a Map to store children nodes and a boolean to mark the end of a word. Insert each character by creating new nodes if needed.

2

Insert given words into the Trie

Create a variable called words as an array of strings with these exact values: "cat", "car", "dog", "door". Then create a variable called trie as a new instance of the Trie class. Use a for loop with variable word to iterate over words and insert each word into trie using the insert method.

DSA Typescript

class TrieNode {
    children: Map;
    isEndOfWord: boolean;

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

class Trie {
    root: TrieNode;

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

    insert(word: string): void {
        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;
    }
}

// Create words array and insert each word into trie
// Your code here

Hint

Create the array with exact words and loop through it to insert each word into the trie.

3

Add search method to Trie class

Add a method called search to the Trie class that takes a word string and returns a boolean. The method should start from this.root and for each character in word, check if the character exists in the current node's children. If not, return false. If all characters are found, return the isEndOfWord value of the last node.

DSA Typescript

class TrieNode {
    children: Map;
    isEndOfWord: boolean;

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

class Trie {
    root: TrieNode;

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

    insert(word: string): void {
        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;
    }

    // Add search method below
    // Your code here
}

const words: string[] = ["cat", "car", "dog", "door"];
const trie = new Trie();
for (const word of words) {
    trie.insert(word);
}

Hint

Traverse the trie nodes for each character. If a character is missing, return false. After the loop, return if the last node marks the end of a word.

4

Search for words and print results

Use console.log to print the result of trie.search("car") and trie.search("cow"). The output should be true for "car" and false for "cow".

DSA Typescript

class TrieNode {
    children: Map;
    isEndOfWord: boolean;

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

class Trie {
    root: TrieNode;

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

    insert(word: string): void {
        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;
    }

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

const words: string[] = ["cat", "car", "dog", "door"];
const trie = new Trie();
for (const word of words) {
    trie.insert(word);
}

// Print search results for "car" and "cow"
// Your code here

Hint

Use console.log to print the boolean results of searching "car" and "cow" in the trie.

Practice

1. What does the search operation in a Trie data structure do?

easy

A. Checks if a given word exists in the Trie

B. Deletes a word from the Trie

C. Inserts a new word into the Trie

D. Counts the total words stored in the Trie

Solution

1. Step 1: Understand the purpose of search in Trie

   The search operation is designed to check if a specific word is present in the Trie data structure.

2. Step 2: Differentiate from other operations

   Insertion adds words, deletion removes words, and counting totals words, but search only checks existence.

3. Final Answer:

   Checks if a given word exists in the Trie -> Option A

4. Quick Check:

   Search = Check existence [OK]

Hint: Search checks presence of word, not insertion or deletion [OK]

Common Mistakes:

• Confusing search with insert operation
• Thinking search deletes words
• Assuming search counts words

2. Which of the following is the correct TypeScript method signature for a Trie search function that returns a boolean?

easy

A. search(word: boolean): boolean

B. search(word: number): string

C. search(word: string): void

D. search(word: string): boolean

Solution

1. Step 1: Identify input and output types for search

   The search method takes a word as a string and returns true or false, so input is string and output is boolean.

2. Step 2: Match method signature with correct types

   Only search(word: string): boolean matches the expected input and output types.

3. Final Answer:

   search(word: string): boolean -> Option D

4. Quick Check:

   Input string, output boolean [OK]

Hint: Search takes string, returns true/false [OK]

Common Mistakes:

• Using wrong input type like number or boolean
• Returning void instead of boolean
• Confusing return type with string

3. Given the following TypeScript Trie search code, what will be the output?

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

medium

A. true\ntrue

B. true\nfalse

C. false\ntrue

D. false\nfalse

Solution

1. Step 1: Check inserted words in Trie

   The words 'cat', 'car', and 'dog' are inserted into the Trie.

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

   'car' exists in the Trie, so search returns true. 'cap' was not inserted, so search returns false.

3. Final Answer:

   true\nfalse -> Option B

4. Quick Check:

   Inserted words found, missing words not found [OK]

Hint: Inserted words return true, others false [OK]

Common Mistakes:

• Assuming 'cap' is found because it starts like 'car'
• Mixing true/false order in output
• Forgetting to insert words before search

4. Identify the bug in this TypeScript Trie search method:

search(word: string): boolean {
  let node = this.root;
  for (let i = 0; i <= word.length; i++) {
    const char = word[i];
    if (!node.children.has(char)) return false;
    node = node.children.get(char)!;
  }
  return node.isEndOfWord;
}

medium

A. Loop condition should be i < word.length, not <=

B. Missing check for empty string input

C. Should return true before loop ends

D. Incorrect use of non-null assertion operator (!)

Solution

1. Step 1: Analyze loop boundary in search method

   The loop runs from i = 0 to i <= word.length, which means it accesses word[word.length], an undefined index.

2. Step 2: Correct loop condition to avoid out-of-bounds

   The loop should run while i < word.length to access valid characters only.

3. Final Answer:

   Loop condition should be i < word.length, not <= -> Option A

4. Quick Check:

   Loop boundary off by one [OK]

Hint: Loop over characters with i < length, not <= length [OK]

Common Mistakes:

• Using <= causes undefined access
• Ignoring empty string edge case
• Misusing non-null assertion without checks

5. You want to modify a Trie search method to support prefix search (check if any word starts with given prefix). Which change is correct?

hard

A. Return true only if prefix is a complete word (isEndOfWord true)

B. Return false if prefix length is less than 3 characters

C. Return true as soon as all prefix characters are found, without checking isEndOfWord

D. Return true only if prefix matches exactly one word

Solution

1. Step 1: Understand prefix search goal

   Prefix search should confirm if any word starts with the given prefix, not necessarily a complete word.

2. Step 2: Adjust search logic for prefix

   Return true once all prefix characters are found in sequence, without requiring isEndOfWord to be true.

3. Final Answer:

   Return true as soon as all prefix characters are found, without checking isEndOfWord -> Option C

4. Quick Check:

   Prefix found means true, no full word check needed [OK]

Hint: Prefix search stops after matching prefix, ignores full word flag [OK]

Common Mistakes:

• Checking isEndOfWord for prefix search
• Rejecting short prefixes arbitrarily
• Requiring prefix to match exactly one word