Group Anagrams in JavaScript

Given an array of strings, group the anagrams together. You can return the answer in any order.

An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, using all the original letters exactly once.

Example:

Input:   strings = ["eat","tea","tan","ate","nat","bat"]

Output:  [["bat"],["nat","tan"],["ate","eat","tea"]]

Note:

For this lesson, your algorithm should run in O(n * log n * L * log L) time and use O(n * L) extra space.
(There are faster solutions which we will discuss in future lessons)

Understanding the Problem

The core challenge of this problem is to identify and group words that are anagrams of each other. An anagram is a rearrangement of the letters of a word to form another word. For example, "eat" and "tea" are anagrams because they contain the same letters.

This problem is significant in various applications such as text analysis, cryptography, and natural language processing where identifying similar patterns is crucial.

Potential pitfalls include not handling different cases (e.g., uppercase vs lowercase) and not efficiently grouping the anagrams.

Approach

To solve this problem, we need to identify a way to group words that are anagrams. A naive solution might involve comparing each word with every other word, but this would be inefficient.

A more optimized approach involves sorting the characters of each word. Anagrams, when sorted, will result in the same string. For example, "eat" and "tea" both become "aet" when sorted. We can use this property to group anagrams together.

Naive Solution

The naive solution involves comparing each word with every other word to check if they are anagrams. This approach is not optimal due to its high time complexity.

Optimized Solution

We can use a hash map to group words by their sorted character strings. The key will be the sorted string, and the value will be a list of words that match this sorted string.

Algorithm

1. Initialize an empty hash map.

2. Iterate through each word in the input array.

3. Sort the characters of the word to form the key.

4. If the key is not in the hash map, add it with an empty list as its value.

5. Append the original word to the list corresponding to the key.

6. Return the values of the hash map as the grouped anagrams.

Code Implementation


// Function to group anagrams
function groupAnagrams(strs) {
    // Initialize a hash map to store grouped anagrams
    const map = new Map();

    // Iterate through each word in the input array
    for (let str of strs) {
        // Sort the characters of the word to form the key
        const sortedStr = str.split('').sort().join('');

        // If the key is not in the hash map, add it with an empty list as its value
        if (!map.has(sortedStr)) {
            map.set(sortedStr, []);
        }

        // Append the original word to the list corresponding to the key
        map.get(sortedStr).push(str);
    }

    // Return the values of the hash map as the grouped anagrams
    return Array.from(map.values());
}

// Example usage
const strings = ["eat", "tea", "tan", "ate", "nat", "bat"];
console.log(groupAnagrams(strings));

Complexity Analysis

The time complexity of this solution is O(n * log n * L * log L), where n is the number of words and L is the maximum length of a word. This is because sorting each word takes O(L * log L) time, and we do this for each of the n words.

The space complexity is O(n * L) because we store each word in the hash map.

Edge Cases

Potential edge cases include:

Empty input array: The function should return an empty array.
Single word input: The function should return an array with one group containing the single word.
Words with different cases: Ensure the function handles case sensitivity correctly.

Testing

To test the solution comprehensively, consider the following test cases:

Simple cases with a few anagrams.
Cases with no anagrams.
Cases with multiple anagram groups.
Edge cases as mentioned above.

Thinking and Problem-Solving Tips

When approaching such problems, it's essential to:

Understand the problem requirements and constraints.
Think about properties of the problem (e.g., sorted characters for anagrams).
Consider different approaches and their trade-offs.
Write clean, readable code and test it thoroughly.

Conclusion

Grouping anagrams is a common problem that can be efficiently solved using hash maps and sorting. Understanding the properties of anagrams and leveraging data structures like hash maps can lead to optimal solutions.

Practice and exploration of similar problems can help improve problem-solving skills and algorithmic thinking.

Group Anagrams in JavaScript (O(n * log n * L * log L) Time Complexity)