Group Anagrams Using Hash Map in DSA Rust - Build from Scratch

Group Anagrams Using Hash Map

📖 Scenario: You work at a word game company. You need to group words that are anagrams of each other to help players find word matches quickly.

🎯 Goal: Build a Rust program that groups a list of words into groups where each group contains words that are anagrams of each other.

📋 What You'll Learn

Create a vector of strings called words with the exact words: "eat", "tea", "tan", "ate", "nat", "bat"

Create a mutable hash map called anagram_map to store groups of anagrams

Use a for loop with variable word to iterate over words

Inside the loop, create a sorted string called sorted_word from the characters of word

Insert word into anagram_map using sorted_word as the key

Print the groups of anagrams stored in anagram_map

💡 Why This Matters

🌍 Real World

Grouping anagrams helps in word games, spell checkers, and search engines to find related words quickly.

💼 Career

Understanding hash maps and string manipulation is essential for software engineers working on text processing and data grouping tasks.

1

Create the list of words

Create a vector of strings called words with these exact words: "eat", "tea", "tan", "ate", "nat", "bat"

DSA Rust

# Create the vector words with the given strings
# Your code here

Hint

Use let words = vec!["eat", "tea", "tan", "ate", "nat", "bat"]; to create the vector.

2

Create the hash map to group anagrams

Add a mutable hash map called anagram_map that maps String keys to vectors of strings (Vec<&str>) to group the anagrams.

DSA Rust

fn main() {
    let words = vec!["eat", "tea", "tan", "ate", "nat", "bat"];
    // Create mutable hash map anagram_map
    // Your code here
}

Hint

Use let mut anagram_map: HashMap> = HashMap::new(); to create the map.

3

Group words by sorted characters

Use a for loop with variable word to iterate over words. Inside the loop, create a sorted string called sorted_word by sorting the characters of word. Then insert word into anagram_map using sorted_word as the key.

DSA Rust

use std::collections::HashMap;

fn main() {
    let words = vec!["eat", "tea", "tan", "ate", "nat", "bat"];
    let mut anagram_map: HashMap> = HashMap::new();

    // Loop over words and group anagrams
    // Your code here
}

Hint

Use for word in &words to loop. Sort characters with chars.sort_unstable(). Use anagram_map.entry(sorted_word).or_insert(Vec::new()).push(word); to add words.

4

Print the grouped anagrams

Print the groups of anagrams stored in anagram_map using a for loop with variables key and group to iterate over anagram_map.iter(). Print each group vector.

DSA Rust

use std::collections::HashMap;

fn main() {
    let words = vec!["eat", "tea", "tan", "ate", "nat", "bat"];
    let mut anagram_map: HashMap> = HashMap::new();

    for word in &words {
        let mut chars: Vec = word.chars().collect();
        chars.sort_unstable();
        let sorted_word: String = chars.into_iter().collect();
        anagram_map.entry(sorted_word).or_insert(Vec::new()).push(word);
    }

    // Print each group of anagrams
    // Your code here
}

Hint

Use for (key, group) in anagram_map.iter() and println!("{:?}", group); to print groups.

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