Trie Node Design and Initialization in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a TrieNode struct with a children map.

DSA Go

type TrieNode struct {
    children map[rune]*[1]
    isEnd bool
}

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

ANode

BTrieNode

CTreeNode

DTrie

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different struct name for children map values.

Not using pointers for child nodes.

The children map should hold pointers to TrieNode structs to represent child nodes.

2fill in blank

medium

Complete the code to initialize a new TrieNode with an empty children map.

DSA Go

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

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

ATrie

BNode

CTreeNode

DTrieNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using make with wrong type.

Not initializing the map, causing nil map errors.

The children map must be initialized with make for the TrieNode type.

3fill in blank

hard

Fix the error in the code to add a child node for a character key.

DSA Go

func (node *TrieNode) AddChild(ch rune) {
    if node.children == nil {
        node.children = make(map[rune]*[1])
    }
    node.children[ch] = NewTrieNode()
}

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

ATrieNode

BNode

CTreeNode

DTrie

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect struct name in map initialization.

Not initializing the map before adding children.

The children map must hold pointers to TrieNode structs.

4fill in blank

hard

Fill both blanks to check if a child node exists and return it.

DSA Go

func (node *TrieNode) GetChild(ch rune) (*TrieNode, bool) {
    child, [1] := node.children[ch]
    return child, [2]
}

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

Aok

Bexists

Cfound

Dpresent

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names other than 'ok' for the comma-ok idiom.

Returning the wrong variable for existence check.

The comma-ok idiom uses 'ok' to check if a key exists in a map.

5fill in blank

hard

Fill all three blanks to insert a word into the trie.

DSA Go

func (node *TrieNode) Insert(word string) {
    current := node
    for _, ch := range word {
        child, [1] := current.children[ch]
        if ![2] {
            child = NewTrieNode()
            current.children[ch] = [3]
        }
        current = child
    }
    current.isEnd = true
}

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

Aok

Bexists

Cchild

Dpresent

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names for existence check.

Not assigning the new node to the children map.

Use 'ok' for existence check and assign the new node to current.children[ch].

Practice

1. What is the primary purpose of a Trie node in a Trie data structure?

easy

A. To store characters and links to child nodes for prefix-based search

B. To store integer values for sorting

C. To hold a single string value only

D. To act as a queue for BFS traversal

Solution

1. Step 1: Understand Trie node role

   A Trie node stores characters and links to child nodes to represent prefixes of words.

2. Step 2: Compare options

   Only To store characters and links to child nodes for prefix-based search correctly describes storing characters and child links for prefix search.

3. Final Answer:

   To store characters and links to child nodes for prefix-based search -> Option A

4. Quick Check:

   Trie node = prefix storage [OK]

Hint: Trie nodes hold characters and children for prefix search [OK]

Common Mistakes:

• Thinking Trie nodes store whole words only
• Confusing Trie nodes with array or queue structures
• Assuming Trie nodes store integer values

2. Which of the following is the correct way to declare a Trie node struct in Go with children for 26 lowercase letters and a boolean to mark end of word?

easy

A. type TrieNode struct { children [26]*TrieNode; isEnd bool }

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

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

D. type TrieNode struct { children [26]TrieNode; isEnd string }

Solution

1. Step 1: Check children type

   Children should be an array of pointers to TrieNode for 26 letters: [26]*TrieNode.

2. Step 2: Check isEnd type

   isEnd should be boolean to mark word end.

3. Final Answer:

   type TrieNode struct { children [26]*TrieNode; isEnd bool } -> Option A

4. Quick Check:

   Children as pointer array + bool isEnd = type TrieNode struct { children [26]*TrieNode; isEnd bool } [OK]

Hint: Use array of pointers and bool for end marker [OK]

Common Mistakes:

• Using slice instead of fixed array for children
• Using int or string instead of bool for isEnd
• Using map with wrong key type

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

type TrieNode struct {
  children [26]*TrieNode
  isEnd bool
}

func main() {
  root := &TrieNode{}
  if root.children[0] == nil {
    println("No child at index 0")
  } else {
    println("Child exists at index 0")
  }
}

medium

A. Compilation error

B. No child at index 0

C. Child exists at index 0

D. Runtime panic

Solution

1. Step 1: Understand initialization of children array

   When root is created, children array elements are nil pointers by default.

2. Step 2: Check condition in if statement

   root.children[0] is nil, so condition is true and prints "No child at index 0".

3. Final Answer:

   No child at index 0 -> Option B

4. Quick Check:

   Uninitialized children = nil pointers [OK]

Hint: Uninitialized pointer arrays have nil elements [OK]

Common Mistakes:

• Assuming children are auto-initialized with nodes
• Expecting compilation or runtime errors
• Confusing zero values for pointers

4. Identify the error in this Go code snippet for initializing a Trie node:

type TrieNode struct {
  children [26]*TrieNode
  isEnd bool
}

func NewNode() *TrieNode {
  node := TrieNode{}
  node.isEnd = false
  return &node
}

medium

A. isEnd should be true by default

B. Children array is not initialized with pointers

C. Function returns a pointer to a local variable

D. Syntax error in struct declaration

Solution

1. Step 1: Analyze the NewNode function

   The function creates a local struct variable node and returns its address &node.

2. Step 2: Identify the problem

   Returning the pointer to a local variable risks a dangling pointer after the function exits, even though Go's escape analysis heap-allocates it; it's poor practice and should use &TrieNode{} instead.

3. Final Answer:

   Function returns a pointer to a local variable -> Option C

4. Quick Check:

   Return &local_var = bad practice [OK]

Hint: Avoid returning pointers to local variables [OK]

Common Mistakes:

• Thinking children must be explicitly initialized
• Confusing pointer nil with error
• Assuming isEnd default must be true

5. You want to initialize a Trie node in Go that supports Unicode characters instead of just 26 lowercase letters. Which data structure change is best to support this efficiently?

hard

A. Keep children as [26]*TrieNode but convert Unicode to lowercase ASCII

B. Increase children array size to 65536 elements

C. Use slice []*TrieNode with fixed size 26

D. Change children from [26]*TrieNode array to map[rune]*TrieNode

Solution

1. Step 1: Understand Unicode support needs

   Unicode has many characters beyond 26 letters, so fixed array is inefficient.

2. Step 2: Evaluate data structure options

   Using map[rune]*TrieNode allows dynamic keys for any Unicode character efficiently.

3. Step 3: Reject other options

   Array of 65536 is large and wasteful; slice with fixed size 26 is too small; converting Unicode to ASCII loses data.

4. Final Answer:

   Change children from [26]*TrieNode array to map[rune]*TrieNode -> Option D

5. Quick Check:

   Map with rune keys = Unicode support [OK]

Hint: Use map with rune keys for Unicode children [OK]

Common Mistakes:

• Using large fixed arrays wasting memory
• Ignoring Unicode complexity
• Trying to fit Unicode into ASCII-only arrays