Word Search in Trie in DSA Go - Build from Scratch

Word Search in Trie

📖 Scenario: You are building a simple word search tool that can quickly check if a word exists in a dictionary. To do this efficiently, you will use a Trie data structure, which stores words in a tree-like form.Imagine a phone's autocomplete feature that suggests words as you type. The Trie helps find words fast by sharing common prefixes.

🎯 Goal: Build a Trie to store a list of words, then search for a specific word in the Trie to check if it exists.

📋 What You'll Learn

Create a Trie node structure with children and end-of-word marker

Insert given words into the Trie

Search for a given word in the Trie

Print whether the word exists or not

💡 Why This Matters

🌍 Real World

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

💼 Career

Understanding Tries helps in roles involving search engines, text processing, and efficient data retrieval.

1

Create Trie Node Structure

Create a struct called TrieNode with a field children which is a map from rune to *TrieNode, and a boolean field isEndOfWord.

DSA Go

// Your code here

Hint

Use map[rune]*TrieNode for children to store links to next letters.

2

Initialize Trie Root and Insert Words

Create a variable root of type *TrieNode initialized with an empty children map. Then write a function insertWord that takes root *TrieNode and word string and inserts the word into the Trie by creating nodes as needed.

DSA Go

root := &TrieNode{children: make(map[rune]*TrieNode)}

// Your code here

Hint

Initialize root with an empty map. Loop over each character in word. Create new nodes if missing.

3

Search for a Word in the Trie

Write a function searchWord that takes root *TrieNode and word string and returns bool. It should return true if the word exists in the Trie, otherwise false. Use a loop to traverse the Trie nodes for each character.

DSA Go

func searchWord(root *TrieNode, word string) bool {
    // Your code here
}

Hint

Traverse the Trie for each character. If a character node is missing, return false. After the loop, check if isEndOfWord is true.

4

Print Search Result

In main, call searchWord with root and the word "golang". Print "Found" if it returns true, otherwise print "Not Found".

DSA Go

    // Your code here

Hint

Use if searchWord(root, "golang") then println("Found") else println("Not Found").

Practice

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

easy

A. To reverse words quickly

B. To sort words alphabetically

C. To store words efficiently for quick prefix-based searches

D. To count the frequency of words

Solution

1. Step 1: Understand Trie structure

   A Trie stores characters of words in a tree form, sharing prefixes.

2. Step 2: Identify Trie use in word search

   This structure allows fast prefix checks and word existence queries.

3. Final Answer:

   To store words efficiently for quick prefix-based searches -> Option C

4. Quick Check:

   Trie = prefix search efficiency [OK]

Hint: Trie is best for prefix-based word searches [OK]

Common Mistakes:

• Confusing Trie with sorting structures
• Thinking Trie counts word frequency
• Assuming Trie reverses words

2. Which of the following Go code snippets correctly initializes an empty Trie node struct with a children map and end-of-word flag?

easy

A. type TrieNode struct { children map[string]TrieNode; isEnd bool }
root := TrieNode{children: map[string]TrieNode{}, isEnd: false}

B. type TrieNode struct { children []TrieNode; isEnd int }
root := TrieNode{children: []TrieNode{}, isEnd: 0}

C. type TrieNode struct { children map[rune]TrieNode; isEnd bool }
root := &TrieNode{children: make(map[rune]TrieNode), isEnd: false}

D. type TrieNode struct { children map[rune]*TrieNode; isEnd bool }
root := &TrieNode{children: make(map[rune]*TrieNode), isEnd: false}

Solution

1. Step 1: Check struct field types

   Children should be a map from rune to pointer to TrieNode for dynamic nodes.

2. Step 2: Verify initialization syntax

   Use make(map[rune]*TrieNode) and isEnd as bool with false initial value.

3. Final Answer:

   type TrieNode struct { children map[rune]*TrieNode; isEnd bool } root := &TrieNode{children: make(map[rune]*TrieNode), isEnd: false} -> Option D

4. Quick Check:

   Correct map and pointer usage = type TrieNode struct { children map[rune]*TrieNode; isEnd bool } root := &TrieNode{children: make(map[rune]*TrieNode), isEnd: false} [OK]

Hint: Use map[rune]*TrieNode and make() to initialize children [OK]

Common Mistakes:

• Using slice instead of map for children
• Using non-pointer TrieNode in map values
• Incorrect map key type (string instead of rune)

3. Given the following Go code snippet for searching a word in a Trie, what will be the output if the word "cat" is searched after inserting "car" and "cat"?

func (t *TrieNode) Search(word string) bool {
    node := t
    for _, ch := range word {
        if _, ok := node.children[ch]; !ok {
            return false
        }
        node = node.children[ch]
    }
    return node.isEnd
}

medium

A. true

B. false

C. Compilation error

D. Runtime panic

Solution

1. Step 1: Understand insertion of "car" and "cat"

   Both words share prefix 'ca', nodes created for 'c', 'a', then separate nodes for 'r' and 't' with isEnd true.

2. Step 2: Trace search for "cat"

   Traverse nodes for 'c', 'a', 't' successfully, last node has isEnd true, so returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Word inserted and found = true [OK]

Hint: Search returns true if last node's isEnd is true [OK]

Common Mistakes:

• Assuming search returns true for prefixes only
• Confusing isEnd flag usage
• Thinking search returns true if partial path exists

4. Identify the bug in the following Go code snippet for searching a word in a Trie:

func (t *TrieNode) Search(word string) bool {
    node := t
    for _, ch := range word {
        if node.children[ch] == nil {
            return false
        }
        node = node.children[ch]
    }
    return true
}

medium

A. Returns true even if the word is only a prefix, not a full word

B. Panics if children map is nil

C. Does not check for nil children map before access

D. Incorrect loop variable type causes compilation error

Solution

1. Step 1: Analyze search return condition

   Function returns true after traversing all characters without checking isEnd flag.

2. Step 2: Understand consequence of missing isEnd check

   Words that are prefixes but not complete words will incorrectly return true.

3. Final Answer:

   Returns true even if the word is only a prefix, not a full word -> Option A

4. Quick Check:

   Missing isEnd check causes false positives [OK]

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

Common Mistakes:

• Forgetting to check isEnd flag
• Assuming traversal success means word exists
• Ignoring nil map checks (not in this code)

5. You have a list of words: ["apple", "app", "application", "bat", "bath", "baton"]. You want to build a Trie and then search for the word "bat". Which of the following statements is true about the search result and the Trie structure after insertion?

hard

A. Searching "bat" returns false because "bat" is a prefix of "bath" and "baton"

B. Searching "bat" returns true; nodes for 'b', 'a', 't' share prefixes with other words

C. Trie stores each word as a separate branch without shared nodes

D. Searching "bat" returns true only if "bat" is inserted last

Solution

1. Step 1: Insert all words into Trie

   Words share prefixes: "app" and "apple" share 'app', "bat", "bath", "baton" share 'bat'.

2. Step 2: Search for "bat"

   Since "bat" is inserted, its node's isEnd is true, so search returns true.

3. Final Answer:

   Searching "bat" returns true; nodes for 'b', 'a', 't' share prefixes with other words -> Option B

4. Quick Check:

   Shared prefix nodes and isEnd true = Searching "bat" returns true; nodes for 'b', 'a', 't' share prefixes with other words [OK]

Hint: Shared prefixes save space; isEnd marks full words [OK]

Common Mistakes:

• Thinking prefix words are not found
• Assuming separate branches for each word
• Believing insertion order affects search result