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

Group Anagrams Using Hash Map

📖 Scenario: You work in 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 program that groups a list of words into arrays of anagrams using a hash map (JavaScript object).

📋 What You'll Learn

Create an array called words with the exact words: 'eat', 'tea', 'tan', 'ate', 'nat', 'bat'

Create an empty object called anagramGroups to store grouped anagrams

Use a for loop with variable word to iterate over words

Inside the loop, create a variable sortedWord that holds the letters of word sorted alphabetically

Use sortedWord as a key in anagramGroups to group words

Print the values of anagramGroups as an array of arrays

💡 Why This Matters

🌍 Real World

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

💼 Career

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

1

Create the list of words

Create an array called words with these exact strings: 'eat', 'tea', 'tan', 'ate', 'nat', 'bat'

DSA Javascript

# Create the array words with the given strings
// Your code here

Hint

Use square brackets [] to create an array and separate words with commas.

2

Create the hash map to hold groups

Create an empty object called anagramGroups to store grouped anagrams

DSA Javascript

const words = ['eat', 'tea', 'tan', 'ate', 'nat', 'bat'];
// Create an empty object anagramGroups
// Your code here

Hint

Use curly braces {} to create an empty object.

3

Group words by sorted letters

Use a for loop with variable word to iterate over words. Inside the loop, create a variable sortedWord that holds the letters of word sorted alphabetically using word.split('').sort().join(''). Then, if sortedWord is not a key in anagramGroups, create it with an empty array. Finally, push word into anagramGroups[sortedWord].

DSA Javascript

const words = ['eat', 'tea', 'tan', 'ate', 'nat', 'bat'];
const anagramGroups = {};
// Use a for loop with variable word to iterate over words
// Inside the loop, create sortedWord by sorting letters of word
// Group words in anagramGroups by sortedWord
// Your code here

Hint

Use word.split('') to split letters, .sort() to sort, and .join('') to join back.

Check if the key exists in the object before adding.

4

Print the grouped anagrams

Print the values of anagramGroups as an array of arrays using console.log(Object.values(anagramGroups))

DSA Javascript

const words = ['eat', 'tea', 'tan', 'ate', 'nat', 'bat'];
const anagramGroups = {};
for (const word of words) {
    const sortedWord = word.split('').sort().join('');
    if (!anagramGroups[sortedWord]) {
        anagramGroups[sortedWord] = [];
    }
    anagramGroups[sortedWord].push(word);
}
// Print the grouped anagrams
// Your code here

Hint

Use Object.values(anagramGroups) to get all grouped arrays.

Practice

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

easy

A. Group words by their length using a hash map

B. Count the number of vowels in each word and group by count

C. Use the first letter of each word as the key in the hash map

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

Solution

1. Step 1: Understand anagrams

   Anagrams are words with the same letters in different orders, so sorting letters gives a unique 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 can be grouped.

3. Final Answer:

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

4. Quick Check:

   Sorted word keys group anagrams = C [OK]

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

Common Mistakes:

• Grouping by word length only
• Using first letter as key
• Counting vowels instead of letters

2. Which of the following JavaScript code snippets correctly initializes an empty hash map to group anagrams?

easy

A. const map = {};

B. const map = Map();

C. const map = [];

D. const map = new Set();

Solution

1. Step 1: Identify hash map initialization in JavaScript

   JavaScript objects ({}) are commonly used as hash maps for key-value pairs.

2. Step 2: Analyze the options

   {} creates a simple hash map using bracket notation like map[key]. Map() without new throws TypeError. [] creates an array unsuitable for key-value pairs. new Set() stores unique values, not mappings.

3. Final Answer:

   const map = {}; -> Option A

4. Quick Check:

   Object literal {} is simplest hash map = A [OK]

Hint: Use {} to create a simple hash map in JavaScript [OK]

Common Mistakes:

• Using array [] instead of object
• Using Set which doesn't store key-value pairs
• Confusing Map and object initialization

3. What is the output of the following code?

function groupAnagrams(words) {
  const map = {};
  for (const word of words) {
    const sorted = word.split('').sort().join('');
    if (!map[sorted]) map[sorted] = [];
    map[sorted].push(word);
  }
  return Object.values(map);
}

console.log(groupAnagrams(['bat', 'tab', 'eat', 'tea', 'ate']));

medium

A. SyntaxError

B. [['bat'], ['tab'], ['eat'], ['tea'], ['ate']]

C. [['bat', 'tab'], ['eat', 'tea', 'ate']]

D. [['bat', 'tab', 'eat', 'tea', 'ate']]

Solution

1. Step 1: Sort each word and group in map

   Words 'bat' and 'tab' both sort to 'abt', so grouped together. 'eat', 'tea', 'ate' all sort to 'aet', grouped together.

2. Step 2: Return grouped anagrams as array of arrays

   Object.values(map) returns arrays of grouped words: [['bat', 'tab'], ['eat', 'tea', 'ate']].

3. Final Answer:

   [['bat', 'tab'], ['eat', 'tea', 'ate']] -> Option C

4. Quick Check:

   Sorted keys group words = [['bat','tab'],['eat','tea','ate']] [OK]

Hint: Sort words, group by sorted key, return grouped arrays [OK]

Common Mistakes:

• Returning flat list instead of grouped arrays
• Not sorting words before grouping
• Syntax errors from missing brackets

4. Find the error in this code snippet for grouping anagrams:

function groupAnagrams(words) {
  const map = {};
  for (const word of words) {
    const sorted = word.sort().join('');
    if (!map[sorted]) map[sorted] = [];
    map[sorted].push(word);
  }
  return Object.values(map);
}

medium

A. map should be initialized as a Map object

B. word.sort() is invalid because word is a string, not an array

C. Missing return statement

D. Using Object.values on map is incorrect

Solution

1. Step 1: Identify the error in sorting

   word is a string, and strings do not have a sort() method. It must be split into an array first.

2. Step 2: Correct approach to sort letters

   Use word.split('').sort().join('') to sort letters of the string correctly.

3. Final Answer:

   word.sort() is invalid because word is a string, not an array -> Option B

4. Quick Check:

   Strings need split() before sort() = B [OK]

Hint: Split string to array before sorting letters [OK]

Common Mistakes:

• Calling sort() directly on string
• Not splitting string before sorting
• Confusing Map object with plain object

5. Given the input array ['listen', 'silent', 'enlist', 'google', 'gogole', 'abc', 'cab'], which of the following is the correct grouped anagrams output using a hash map approach?

hard

A. [['listen', 'silent', 'enlist'], ['google', 'gogole'], ['abc', 'cab']]

B. [['listen', 'silent'], ['enlist', 'google'], ['gogole', 'abc', 'cab']]

C. [['listen'], ['silent'], ['enlist'], ['google'], ['gogole'], ['abc'], ['cab']]

D. [['listen', 'silent', 'enlist', 'google', 'gogole', 'abc', 'cab']]

Solution

1. Step 1: Sort each word to find keys

   'listen', 'silent', 'enlist' all sort to 'eilnst'; 'google', 'gogole' sort to 'eggloo'; 'abc', 'cab' sort to 'abc'.

2. Step 2: Group words by sorted keys

   Group words with same sorted key together: [['listen', 'silent', 'enlist'], ['google', 'gogole'], ['abc', 'cab']].

3. Final Answer:

   [['listen', 'silent', 'enlist'], ['google', 'gogole'], ['abc', 'cab']] -> Option A

4. Quick Check:

   Sorted keys group anagrams correctly = A [OK]

Hint: Sort letters, group by key, collect arrays [OK]

Common Mistakes:

• Mixing groups with different sorted keys
• Grouping by word length instead of letters
• Returning flat list instead of grouped arrays