Group Anagrams Using Hash Map in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize an empty hash map for grouping anagrams.

DSA Javascript

const map = new [1]();

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AMap

BSet

CArray

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using Array or Set instead of Map for key-value storage.

Using Object but forgetting it doesn't preserve insertion order.

We use a Map to store groups of anagrams with keys as sorted strings.

2fill in blank

medium

Complete the code to sort the characters of the string 'word' to create the key.

DSA Javascript

const key = word.split('').[1]().join('');

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Areverse

Bmap

Cfilter

Dsort

Attempts:

3 left

💡 Hint

Common Mistakes

Using reverse() which reverses but does not sort.

Using map() or filter() which do not sort.

Sorting characters alphabetically groups anagrams under the same key.

3fill in blank

hard

Fix the error in checking if the map has the key and adding the word to the group.

DSA Javascript

if (!map.[1](key)) {
  map.set(key, []);
}
map.get(key).push(word);

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Acontains

Bexists

Chas

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using contains() or includes() which are not Map methods.

Using exists() which is not a JavaScript method.

The Map method to check key existence is has().

4fill in blank

hard

Fill both blanks to convert the map values to an array of grouped anagrams.

DSA Javascript

const result = Array.[1](map.[2]());

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Afrom

Bvalues

Ckeys

Dentries

Attempts:

3 left

💡 Hint

Common Mistakes

Using map.keys() or map.entries() which do not give groups directly.

Using Array.entries() which is not a function.

Array.from() converts iterable map.values() to an array of groups.

5fill in blank

hard

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

DSA Javascript

function groupAnagrams(strs) {
  const map = new [1]();
  for (const word of strs) {
    const key = word.split('').[2]().join('');
    if (!map.[3](key)) {
      map.set(key, []);
    }
    map.get(key).push(word);
  }
  return Array.from(map.values());
}

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

AMap

Bsort

Chas

DSet

Attempts:

3 left

💡 Hint

Common Mistakes

Using Set instead of Map for grouping.

Using reverse instead of sort for keys.

Using contains or exists instead of has.

Use Map to store groups, sort to create keys, and has to check keys.

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