Group Anagrams Using Hash Map in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new empty HashMap for grouping anagrams.

DSA Rust

let mut map: std::collections::HashMap<String, Vec<String>> = [1];

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

AString::new()

BVec::new()

Cstd::collections::HashMap::new()

DHashSet::new()

Attempts:

3 left

💡 Hint

Common Mistakes

Using Vec::new() instead of HashMap::new() causes type mismatch.

Using HashSet::new() is wrong because we need key-value pairs.

We use HashMap::new() to create an empty hash map for grouping anagrams.

2fill in blank

medium

Complete the code to sort the characters of the word to use as a key.

DSA Rust

let mut chars: Vec<char> = word.chars().collect();
chars.[1]();
let key: String = chars.into_iter().collect();

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Ashuffle

Bsort_unstable

Creverse

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using reverse() reverses order but does not sort.

Using pop() removes elements, not sorting.

We use sort_unstable() to sort characters efficiently for the anagram key.

3fill in blank

hard

Fix the error in inserting the word into the map for the sorted key.

DSA Rust

map.entry(key).[1](Vec::new()).push(word.clone());

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Aor_insert

Binsert

Cget

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using insert() replaces the entire entry and returns an Option.

Using get() returns an immutable reference, so push() fails.

or_insert() inserts a new vector if the key is missing and returns a mutable reference to it.

4fill in blank

hard

Fill both blanks to collect grouped anagrams into a vector of vectors.

DSA Rust

let result: Vec<Vec<String>> = map.[1]().[2](|(_, group)| group.clone()).collect();

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Ainto_iter

Biter

Cmap

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using iter() borrows the map, causing lifetime issues.

Using filter() is for filtering, not mapping.

We use into_iter() to consume the map and map() to extract the groups.

5fill in blank

hard

Fill all three blanks to complete the function that groups anagrams.

DSA Rust

fn group_anagrams(strs: Vec<String>) -> Vec<Vec<String>> {
    let mut map = std::collections::HashMap::new();
    for word in strs {
        let mut chars: Vec<char> = word.chars().[1]();
        chars.[2]();
        let key: String = chars.into_iter().collect();
        map.entry(key).[3](Vec::new()).push(word);
    }
    map.into_iter().map(|(_, group)| group).collect()
}

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Acollect

Bsort_unstable

Cor_insert

Dcollect_vec

Attempts:

3 left

💡 Hint

Common Mistakes

Using collect_vec() is not a standard method.

Failing to sort the characters results in incorrect anagram groups.

We use collect() to gather characters into a vector, sort_unstable() to sort them for the anagram key, and or_insert() to insert or get the group vector.

Practice

1. What is the main idea behind grouping anagrams using a hash map?

easy

A. Use the length of words as keys to group them

B. Store words in a list without any grouping

C. Group words by their first letter only

D. Use sorted strings as keys to group words with the same letters

Solution

1. Step 1: Understand anagram grouping

   Anagrams have the same letters in different orders, so sorting letters gives a common key.

2. Step 2: Use sorted string as hash map key

   By sorting each word and using it as a key, all anagrams map to the same key and group together.

3. Final Answer:

   Use sorted strings as keys to group words with the same letters -> Option D

4. Quick Check:

   Sorted string key groups anagrams [OK]

Hint: Sort each word to find its anagram group key [OK]

Common Mistakes:

• Grouping by word length only
• Using first letter as key
• Not sorting letters before grouping

2. Which Rust code snippet correctly creates a hash map to group anagrams by sorted keys?

easy

A. let mut map: HashMap = HashMap::new();

B. let map = Vec::new();

C. let mut map: HashMap = HashMap::new();

D. let mut map: HashMap = HashMap::new();

Solution

1. Step 1: Identify correct hash map type

   We need keys as sorted strings and values as vectors of strings to hold grouped anagrams.

2. Step 2: Match Rust syntax for hash map

   HashMap correctly maps sorted keys to lists of words.

3. Final Answer:

   let mut map: HashMap = HashMap::new(); -> Option A

4. Quick Check:

   HashMap with String keys and Vec<String> values [OK]

Hint: Use HashMap for grouping anagrams [OK]

Common Mistakes:

• Using Vec instead of HashMap
• Wrong value type (String instead of Vec<String>)
• Incorrect key type (i32 instead of String)

3. What is the output of this Rust code that groups anagrams?

use std::collections::HashMap;

fn group_anagrams(words: Vec<&str>) -> Vec {
    let mut map: HashMap = HashMap::new();
    for word in words {
        let mut chars: Vec<char> = word.chars().collect();
        chars.sort_unstable();
        let key = chars.into_iter().collect::<String>();
        map.entry(key).or_default().push(word.to_string());
    }
    map.into_values().collect()
}

fn main() {
    let input = vec!["eat", "tea", "tan", "ate", "nat", "bat"];
    let result = group_anagrams(input);
    println!("{:?}", result);
}

medium

A. [["eat", "ate", "tea"], ["tan", "nat"], ["bat"]]

B. [["eat"], ["tea"], ["tan"], ["ate"], ["nat"], ["bat"]]

C. [["eat", "tea", "ate"], ["tan", "nat"], ["bat"]]

D. [["eat", "tea"], ["tan"], ["ate", "nat"], ["bat"]]

Solution

1. Step 1: Sort each word to create keys

   "eat", "tea", "ate" all sort to "aet"; "tan", "nat" to "ant"; "bat" to "abt".

2. Step 2: Group words by sorted keys

   Words with same sorted key are grouped: ["eat", "tea", "ate"], ["tan", "nat"], ["bat"].

3. Final Answer:

   [["eat", "tea", "ate"], ["tan", "nat"], ["bat"]] -> Option C

4. Quick Check:

   Sorted keys group anagrams [OK]

Hint: Sort letters and group words by sorted key [OK]

Common Mistakes:

• Not sorting letters before grouping
• Grouping single words separately
• Mixing order of groups incorrectly

4. Identify the bug in this Rust code for grouping anagrams:

use std::collections::HashMap;

fn group_anagrams(words: Vec<&str>) -> Vec {
    let mut map: HashMap = HashMap::new();
    for word in words {
        let mut chars: Vec<char> = word.chars().collect();
        chars.sort(); // Bug here
        let key = chars.into_iter().collect::<String>();
        map.entry(key).or_default().push(word.to_string());
    }
    map.into_values().collect()
}

medium

A. Use sort_unstable() instead of sort() for better performance

B. Change chars.into_iter() to chars.iter()

C. Use a HashSet instead of HashMap

D. Convert word to lowercase before sorting

Solution

1. Step 1: Identify sorting method issue

   Using chars.sort() works but sort_unstable() is preferred for primitive types like char for speed.

2. Step 2: Explain why sort_unstable() is better

   sort_unstable() is faster and sufficient here because order stability is not needed for grouping anagrams.

3. Final Answer:

   Use sort_unstable() instead of sort() for better performance -> Option A

4. Quick Check:

   sort_unstable() improves sorting speed [OK]

Hint: Use sort_unstable() for sorting chars in anagrams [OK]

Common Mistakes:

• Using sort() unnecessarily slowing code
• Changing iterator type incorrectly
• Ignoring case sensitivity issues

5. Given a list of words with mixed case and spaces, how would you modify the Rust code to group anagrams correctly ignoring case and spaces? Example input: ["Listen", "Silent", "en list", "in lets"]

hard

A. Sort letters without any changes to words

B. Convert words to lowercase and remove spaces before sorting letters

C. Use word length as key for grouping

D. Group words by their first character only

Solution

1. Step 1: Normalize words by removing spaces and converting to lowercase

   To group anagrams ignoring case and spaces, clean words by removing spaces and making all letters lowercase.

2. Step 2: Sort letters of normalized words and use as keys

   After normalization, sort letters to get keys that group all anagrams regardless of case or spaces.

3. Final Answer:

   Convert words to lowercase and remove spaces before sorting letters -> Option B

4. Quick Check:

   Normalize words before sorting for correct grouping [OK]

Hint: Lowercase and remove spaces before sorting letters [OK]

Common Mistakes:

• Not normalizing case and spaces
• Using length or first letter as key
• Sorting original words without cleaning