Trie Search Operation in DSA Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Trie data structure?

A Trie is a tree-like data structure used to store a dynamic set of strings where keys are usually strings. Each node represents a character, and paths down the tree represent words.

beginner

How does the search operation work in a Trie?

Search starts at the root and follows nodes matching each character of the search word. If all characters are found and the last node marks the end of a word, the search is successful.

beginner

What does it mean if a node in a Trie has a 'is_end_of_word' flag set to true?

It means that the path from the root to this node forms a complete word stored in the Trie.

intermediate

Why is Trie search operation efficient for prefix matching?

Because it shares common prefixes among words, the search only traverses nodes for the prefix characters once, making prefix queries fast.

intermediate

In Rust, what is a common way to represent children nodes in a Trie?

Children nodes are often stored in a fixed-size array or a hash map keyed by characters, allowing quick access to the next node for a given character.

What does the Trie search operation return if the word is not found?

A False or None

B True

C The last node visited

D The root node

If the word is not found, the search returns false or None indicating the word does not exist in the Trie.

Which of these is NOT a step in Trie search?

A Traverse nodes matching each character

B Return true if all characters matched and end flag is true

C Check if the last node marks end of word

D Sort the children nodes before searching

Sorting children nodes is not required in Trie search; direct access is used.

What data structure is commonly used to store children nodes in a Trie in Rust?

A HashMap or array

B Linked list

C Stack

D Queue

HashMap or fixed-size arrays keyed by characters are common for fast access to children nodes.

If a search word is a prefix of a longer word in the Trie but not marked as a complete word, what does search return?

A Partial match node

B False

C True

D Error

Search returns false because the word is not marked as a complete word even if prefix nodes exist.

What is the time complexity of searching a word of length n in a Trie?

A O(n^2)

B O(log n)

C O(n)

D O(1)

Search time is proportional to the length of the word, O(n), as each character is checked once.

Explain step-by-step how the search operation works in a Trie.

Think about walking down the tree following characters.

Describe how children nodes are stored and accessed in a Rust Trie implementation.

Consider how to find the next letter node quickly.

Practice

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

easy

A. Counts the total words stored in the Trie

B. Inserts a new word into the Trie

C. Checks if a given word exists in the Trie

D. Deletes a word from 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 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 C

4. Quick Check:

   Search = Check existence [OK]

Hint: Search checks presence, 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 Rust function signature for a Trie search method that returns a boolean?

easy

A. fn search(&self, word: &str) -> bool

B. fn search(word: String) -> bool

C. fn search(&mut self, word: &str) -> String

D. fn search(&self, word: &str) -> usize

Solution

1. Step 1: Identify correct method receiver and parameters

   The search method should borrow self immutably (&self) and take a string slice (&str) for the word to search.

2. Step 2: Confirm return type

   Search returns a boolean indicating presence, so return type must be bool.

3. Final Answer:

   fn search(&self, word: &str) -> bool -> Option A

4. Quick Check:

   Immutable borrow + &str + bool return [OK]

Hint: Search uses &self and returns bool [OK]

Common Mistakes:

• Using mutable borrow &mut self unnecessarily
• Returning wrong type like String or usize
• Taking owned String instead of &str

3. Given the following Rust Trie search code snippet, what will be the output when searching for "cat"?

let mut trie = Trie::new();
trie.insert("car");
trie.insert("cat");
trie.insert("cap");
println!("{}", trie.search("cat"));

medium

A. Compilation error

B. false

C. panic at runtime

D. true

Solution

1. Step 1: Analyze inserted words

   The words "car", "cat", and "cap" are inserted into the Trie, so "cat" is present.

2. Step 2: Check search output for "cat"

   Searching "cat" should return true because it was inserted.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Inserted words include "cat" so search returns true [OK]

Hint: Search returns true if word was inserted [OK]

Common Mistakes:

• Assuming search returns false if similar words exist
• Confusing insert and search methods
• Expecting runtime errors without reason

4. Identify the bug in this Rust Trie search method snippet:

fn search(&self, word: &str) -> bool {
    let mut node = &self.root;
    for ch in word.chars() {
        if !node.children.contains_key(&ch) {
            return false;
        }
        node = node.children.get(&ch).unwrap();
    }
    true
}

medium

A. Uses unwrap() which causes panic always

B. Returns true even if word is a prefix but not complete word

C. Does not iterate over characters correctly

D. Incorrect return type

Solution

1. Step 1: Understand search logic

   The code checks if each character exists in children nodes, moving down the Trie.

2. Step 2: Check final return condition

   It returns true after loop without verifying if current node marks end of a complete word.

3. Step 3: Identify bug

   This causes search to return true for prefixes that are not full words.

4. Final Answer:

   Returns true even if word is a prefix but not complete word -> Option B

5. Quick Check:

   Missing end-of-word check causes false positives [OK]

Hint: Check end-of-word flag after traversal [OK]

Common Mistakes:

• Ignoring end-of-word marker in search
• Assuming unwrap() always panics here
• Misunderstanding iteration over chars

5. You want to modify a Trie search operation in Rust to support searching with wildcard character '.' which can match any single letter. Which approach is best to implement this feature?

hard

A. Use recursion to explore all children nodes when '.' is encountered

B. Replace '.' with all alphabets before searching iteratively

C. Ignore '.' and treat it as a normal character

D. Use a hash map to store wildcard positions and skip them

Solution

1. Step 1: Understand wildcard '.' meaning

   The '.' can match any single character, so search must consider all possible children at that position.

2. Step 2: Choose search strategy

   Recursion allows exploring all children nodes when '.' is found, checking all paths.

3. Step 3: Evaluate other options

   Replacing '.' with all alphabets is inefficient; ignoring '.' is incorrect; hash map for positions doesn't solve matching.

4. Final Answer:

   Use recursion to explore all children nodes when '.' is encountered -> Option A

5. Quick Check:

   Recursion handles wildcards by branching [OK]

Hint: Use recursion to handle '.' wildcard in search [OK]

Common Mistakes:

• Ignoring wildcard meaning
• Trying to replace '.' with all letters before search
• Skipping recursive exploration