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Group Anagrams – Python Solution Explained

Problem Overview

The Group Anagrams problem is a common challenge in coding interviews and competitive programming. The goal is to group a list of strings such that all anagrams are placed in the same group. Anagrams are words that contain the same characters but in different orders. For example, given the input ["eat", "tea", "tan", "ate", "nat", "bat"], the expected output is [['eat', 'tea', 'ate'], ['tan', 'nat'], ['bat']].

Approach and Solution

In this blog post, we'll discuss an efficient solution using Python's built-in data structures. The provided code uses a dictionary to group the anagrams. Here’s a step-by-step explanation of the approach:

Code Breakdown

Explanation

  1. Initialization: We use defaultdict from the collections module to create a dictionary (hm) where each key will map to a list of anagrams. This is useful because it automatically initializes an empty list for new keys.

  2. Processing Words: For each word in the input list strs, we sort the characters and join them to form a string (temp). This sorted string serves as a unique identifier for each group of anagrams. For instance, both "eat" and "tea" will be transformed into "aet".

  3. Grouping Anagrams: We then use this sorted string as a key to append the original word into the corresponding list in the dictionary. This way, all anagrams end up in the same list.

  4. Generating the Result: Finally, we convert the dictionary values into a list of lists and return it as the result. Each list contains words that are anagrams of each other.

Advantages of This Approach

  • Efficiency: Sorting each word takes O(klog⁡k) time, where k is the length of the word. Given that we process each word individually, the overall complexity is O(n⋅klog⁡k), where n is the number of words. This is efficient for many practical purposes.

  • Clarity: The use of defaultdict and sorting provides a clear and straightforward method to group anagrams without needing complex data structures.

Conclusion

Link to the problem statement: Group Anagrams

The Group Anagrams problem is a great exercise to understand sorting, dictionary operations, and data grouping. The provided solution efficiently groups anagrams and demonstrates a practical use of Python’s powerful standard library. Whether you're preparing for coding interviews or just honing your problem-solving skills, mastering such problems is invaluable.

Feel free to test this code with different inputs and modify it as needed to fit specific constraints or requirements. Happy coding!

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