Trie Search Operation in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the current character exists in the children map.

DSA Go

if _, ok := node.children[[1]]; !ok {
    return false
}

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Anode

Bword

Ci

Dword[i]

Attempts:

3 left

💡 Hint

Common Mistakes

Using the whole word instead of a single character.

Using the index i directly instead of word[i].

We use word[i] to get the current character to check in the children map.

2fill in blank

medium

Complete the code to move to the next node in the trie for the current character.

DSA Go

node = node.children[[1]]

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Ai

Bnode

Cword[i]

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the index i instead of the character word[i].

Using the whole word instead of a single character.

We use word[i] to get the current character and move to its child node.

3fill in blank

hard

Fix the error in the return statement to check if the word ends here.

DSA Go

return node.[1]

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AisEnd

BisWord

Cend

DwordEnd

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect field names like isEnd or end.

Returning the wrong property that does not indicate word end.

The field isWord indicates if the current node marks the end of a word.

4fill in blank

hard

Fill both blanks to complete the for loop iterating over the word characters.

DSA Go

for [1] := 0; [2] < len(word); [1]++ {
    // loop body
}

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Ai

Bj

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables in initialization and condition.

Using variables not declared in the loop.

The loop variable i is used consistently in initialization and condition.

5fill in blank

hard

Fill all three blanks to complete the search function signature and return type.

DSA Go

func (t *Trie) [1](word string) [2] {
    node := t.root
    for i := 0; i < len(word); i++ {
        if _, ok := node.children[word[i]]; !ok {
            return [3]
        }
        node = node.children[word[i]]
    }
    return node.isWord
}

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

ASearch

Bbool

Cfalse

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect function names.

Returning true instead of false when word not found.

Wrong return type.

The function name is Search, it returns a bool, and returns false if word not found.

Practice

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

easy

A. The number of words stored in the Trie

B. If the Trie is empty

C. If a given word exists in the Trie

D. The length of the longest word 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 stored in the Trie.

2. Step 2: Differentiate from other Trie operations

   Other operations like counting words or checking emptiness are not the purpose of search.

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 if the exact word is stored [OK]

Common Mistakes:

• Confusing search with counting words
• Thinking search checks Trie emptiness
• Assuming search returns word length

2. Which of the following is the correct way to check if a character node exists in a Trie map in Go?

easy

A. if node.children[char] != nil

B. if node.children[char] == nil

C. if node.children.contains(char)

D. if node.children.has(char)

Solution

1. Step 1: Recall Go map access syntax

   In Go, to check if a key exists in a map, you check if the value is not nil (for pointer or map values).

2. Step 2: Apply to Trie children map

   Trie children are stored in a map from rune to *TrieNode, so checking if node.children[char] != nil confirms existence.

3. Final Answer:

   if node.children[char] != nil -> Option A

4. Quick Check:

   Go map key exists check [OK]

Hint: Check map key by comparing to nil in Go [OK]

Common Mistakes:

• Using contains or has methods (not in Go maps)
• Checking for equality to nil incorrectly
• Confusing map key existence with value presence

3. Consider the following Go code snippet for searching a word in a Trie:

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

What will be the output of Search("cat") if the Trie contains the words "car", "cat", and "cap"?

medium

A. compilation error

B. true

C. runtime error

D. false

Solution

1. Step 1: Trace the search for "cat" in the Trie

   The loop checks each character 'c', 'a', 't' in order. Since "cat" is inserted, all nodes exist and node.isEnd is true at 't'.

2. Step 2: Return value after traversal

   Because node.isEnd is true at the last character, the function returns true.

3. Final Answer:

   true -> Option B

4. Quick Check:

   Word "cat" exists in Trie = true [OK]

Hint: Search returns true if last node marks word end [OK]

Common Mistakes:

• Ignoring isEnd flag and returning true always
• Assuming false if any child exists
• Confusing runtime errors with nil checks

4. The following Go code for Trie search has a bug. What is the error?

func (t *Trie) Search(word string) bool {
    node := t.root
    for i := 0; i <= len(word); i++ {
        ch := rune(word[i])
        if node.children[ch] == nil {
            return false
        }
        node = node.children[ch]
    }
    return node.isEnd
}

medium

A. Missing check for empty Trie root

B. Incorrect rune conversion for characters

C. Returning wrong boolean value

D. Index out of range error due to loop condition

Solution

1. Step 1: Analyze the loop condition

   The loop runs from i = 0 to i <= len(word), which means it tries to access word[len(word)] causing index out of range error.

2. Step 2: Correct loop boundary

   The loop should run with i < len(word) to avoid accessing beyond the string length.

3. Final Answer:

   Index out of range error due to loop condition -> Option D

4. Quick Check:

   Loop boundary error causes runtime panic [OK]

Hint: Use i < len(word), not i <= len(word) in loops [OK]

Common Mistakes:

• Using <= instead of < in loop
• Ignoring string length limits
• Assuming rune conversion causes error

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

hard

A. Return true immediately after traversing all prefix characters without checking isEnd

B. Return true only if isEnd is true at last prefix character

C. Return false if any character node is missing, else return false always

D. Return true only if prefix length equals word length stored

Solution

1. Step 1: Understand prefix search goal

   Prefix search should return true if the prefix exists as a path in the Trie, regardless of isEnd flag.

2. Step 2: Modify search to return true after prefix traversal

   After checking all prefix characters exist, return true immediately without checking isEnd.

3. Final Answer:

   Return true immediately after traversing all prefix characters without checking isEnd -> Option A

4. Quick Check:

   Prefix search ignores isEnd, returns true if path exists [OK]

Hint: For prefix, return true after full prefix traversal [OK]

Common Mistakes:

• Checking isEnd for prefix search
• Returning false even if prefix path exists
• Confusing prefix length with word length