Is Group Anagrams easy or hard?

Group Anagrams is generally considered a medium-level problem. The challenge comes from recognizing that anagrams share a canonical representation and using hashing to group them efficiently instead of comparing every pair of strings.

How to solve Group Anagrams in O(n)?

Strict O(n) is not possible because you must inspect each character of every string. However, using a character frequency signature avoids sorting and achieves O(n * k) time, where k is the average string length. Each string is processed once to build a 26-character frequency array used as the hash key.

What is the best approach for Group Anagrams?

The most common approach uses a hash map where the key is the sorted version of each string. After sorting characters in a word, all anagrams produce the same key and are grouped together. This runs in O(n * k log k) time where n is the number of strings and k is the average string length.

What data structure is used in Group Anagrams?

The core data structure is a hash map (dictionary). The key represents the canonical form of the string, such as a sorted string or character frequency signature, and the value stores a list of words that match that key.

What is the time complexity of Group Anagrams?

The typical sorting-based solution runs in O(n * k log k) time because each string must be sorted before grouping. A more optimized approach counts character frequencies and builds a signature key, reducing complexity to O(n * k). Both approaches use O(n * k) space to store grouped strings.

Group Anagrams Python or Java solution approach?

In Python or Java, iterate through the array of strings, compute a key for each string (usually by sorting characters), and store the word in a HashMap or dictionary under that key. After processing all words, return the values of the map as grouped anagrams.

Is Group Anagrams asked at Google, Amazon, or Meta?

Group Anagrams is a common hashing and string manipulation problem frequently asked in coding interviews at companies like Amazon, Google, Meta, and Microsoft. Interviewers use it to evaluate understanding of hash maps, string processing, and algorithmic optimization.

Description Solution Video 8:12

49. Group Anagrams

Medium73.0% acceptance87 companies

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

Example 1:

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

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

Explanation:

There is no string in strs that can be rearranged to form "bat".
The strings "nat" and "tan" are anagrams as they can be rearranged to form each other.
The strings "ate", "eat", and "tea" are anagrams as they can be rearranged to form each other.

Example 2:

Input: strs = [""]

Output: [[""]]

Example 3:

Input: strs = ["a"]

Output: [["a"]]

Constraints: