Trie Insert Operation in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new Trie node.

DSA Go

func newNode() *TrieNode {
    return &TrieNode{
        children: make(map[rune]*TrieNode),
        isEnd: [1],
    }
}

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

Afalse

Bnil

Ctrue

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting isEnd to true for new nodes.

Using nil or 0 instead of a boolean value.

The new Trie node should start with isEnd set to false because it does not represent the end of a word yet.

2fill in blank

medium

Complete the code to check if a child node exists for a character.

DSA Go

if _, ok := current.children[[1]]; !ok {
    current.children[[1]] = newNode()
}

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

Aletter

Bword[i]

Crune

Dchar

Attempts:

3 left

💡 Hint

Common Mistakes

Using an undefined variable like 'rune' or 'letter'.

Using word[i] which is a byte, not rune.

We check if the child node for the current character exists using the variable representing the character, here named 'char'.

3fill in blank

hard

Fix the error in marking the end of a word in the insert function.

DSA Go

current.[1] = true

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

Aend

BisEnd

CisWord

DwordEnd

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect field names like 'end' or 'wordEnd'.

Forgetting to mark the end of the word.

The correct field to mark the end of a word in the Trie node is 'isEnd'.

4fill in blank

hard

Fill both blanks to complete the loop that inserts characters into the Trie.

DSA Go

for _, [1] := range [2] {
    if _, ok := current.children[char]; !ok {
        current.children[char] = newNode()
    }
    current = current.children[char]
}

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

Achar

Bword

Cletter

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined variable names.

Mixing up the order of blanks.

The loop iterates over each character 'char' in the string 'word' to insert it into the Trie.

5fill in blank

hard

Fill all three blanks to complete the insert function for the Trie.

DSA Go

func (t *Trie) Insert([1] string) {
    current := t.root
    for _, [2] := range [1] {
        if _, ok := current.children[[2]]; !ok {
            current.children[[2]] = newNode()
        }
        current = current.children[[2]]
    }
    current.isEnd = true
}

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

Aword

Bchar

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not matching loop variable with map key.

The function takes 'word' as input, iterates over each character 'char' in 'word', and inserts nodes accordingly.

Practice

1. What is the main purpose of the Insert operation in a Trie data structure?

easy

A. To delete a word from the Trie

B. To add a new word by creating nodes for each character

C. To search for a word in the Trie

D. To count the total words stored in the Trie

Solution

1. Step 1: Understand the Insert operation

   The Insert operation adds a word by creating nodes for each character if they don't exist.

2. Step 2: Differentiate from other operations

   Deleting removes words, searching finds words, counting totals words. Insert specifically adds words.

3. Final Answer:

   To add a new word by creating nodes for each character -> Option B

4. Quick Check:

   Insert = Add word nodes [OK]

Hint: Insert means adding nodes for each character [OK]

Common Mistakes:

• Confusing insert with search or delete
• Thinking insert counts words
• Assuming insert modifies existing words

2. Which of the following is the correct way to declare a Trie node struct in Go for insertion?

easy

A. type TrieNode struct { children map[rune]*TrieNode; isEnd bool }

B. type TrieNode struct { children []int; isEnd int }

C. type TrieNode struct { children map[string]int; isEnd string }

D. type TrieNode struct { children []string; isEnd bool }

Solution

1. Step 1: Identify correct children type for TrieNode

   Children should map characters (rune) to TrieNode pointers for branching.

2. Step 2: Check isEnd type

   isEnd is a boolean indicating if node ends a word.

3. Final Answer:

   type TrieNode struct { children map[rune]*TrieNode; isEnd bool } -> Option A

4. Quick Check:

   Children map[rune]*TrieNode and isEnd bool [OK]

Hint: Children map with rune keys and bool isEnd [OK]

Common Mistakes:

• Using slice instead of map for children
• Wrong data types for children or isEnd
• Using string keys instead of rune

3. What will be the output after inserting the words "cat" and "car" into an empty Trie and then checking if the node for 'a' under 'c' has children?

medium

A. nil

B. false

C. true

D. runtime error

Solution

1. Step 1: Insert "cat" and "car" into Trie

   Both words share prefix 'c' -> 'a'. After insertion, node 'a' has children 't' and 'r'.

2. Step 2: Check if node 'a' under 'c' has children

   Since 'a' node has two children nodes ('t' and 'r'), it has children, so true.

3. Final Answer:

   true -> Option C

4. Quick Check:

   Shared prefix node has children = true [OK]

Hint: Shared prefix nodes have children after insert [OK]

Common Mistakes:

• Assuming node 'a' has no children
• Confusing node existence with children presence
• Expecting nil or error instead of true

4. Given this Go code snippet for inserting a word into a Trie, what is the bug?

func (t *TrieNode) Insert(word string) {
    node := t
    for _, ch := range word {
        if node.children[ch] == nil {
            node.children[ch] = &TrieNode{}
        }
        node = node.children[ch]
    }
    node.isEnd = true
}

medium

A. children map is not initialized before use

B. Loop variable ch should be int, not rune

C. isEnd should be set before loop

D. Function should return a value

Solution

1. Step 1: Check initialization of children map

   The children map must be initialized (e.g., make(map[rune]*TrieNode)) before inserting nodes.

2. Step 2: Identify impact of missing initialization

   Without initialization, accessing children[ch] causes runtime panic (nil map assignment).

3. Final Answer:

   children map is not initialized before use -> Option A

4. Quick Check:

   Uninitialized map causes runtime error [OK]

Hint: Always initialize map before inserting keys [OK]

Common Mistakes:

• Ignoring map initialization
• Misunderstanding rune vs int for keys
• Thinking isEnd needs early assignment

5. You want to insert the words ["go", "gone", "guild"] into a Trie. After insertion, how many children does the root node have, and why?

hard

A. 0, because root has no children

B. 3, because there are three words

C. 2, because 'go' and 'guild' share 'g' but 'gone' differs

D. 1, because all words start with 'g'

Solution

1. Step 1: Analyze first characters of all words

   All words start with the letter 'g', so root node will have one child for 'g'.

2. Step 2: Understand Trie root children count

   Root children count equals distinct first letters of inserted words, here only 'g'.

3. Final Answer:

   1, because all words start with 'g' -> Option D

4. Quick Check:

   Root children = distinct first letters = 1 [OK]

Hint: Root children = unique first letters of words [OK]

Common Mistakes:

• Counting words instead of unique first letters
• Assuming root has no children
• Confusing shared prefixes with root children count