Problem

At Notion, you are asked to organize a list of words into groups where each group contains words that are anagrams of one another. Write code that is modular, readable, and easy to test.

Task

Implement a function that takes a list of lowercase strings and returns a list of groups, where each group contains all words that are anagrams. Two words are anagrams if they contain the same characters with the same frequencies.

Formal Specification

• Input: words, a list of strings
• Output: A list of lists of strings, where each inner list contains words that are anagrams
• Words in a group may appear in any order
• The groups themselves may appear in any order

Examples

Example 1

• Input: words = ["eat", "tea", "tan", "ate", "nat", "bat"]
• Output: [["eat", "tea", "ate"], ["tan", "nat"], ["bat"]]
• Explanation: Words with the same sorted-character signature belong to the same group.

Example 2

• Input: words = [""]
• Output: [[""]]
• Explanation: The empty string forms a valid anagram group by itself.

Constraints

• 1 <= len(words) <= 10^4
• 0 <= len(words[i]) <= 100
• words[i] contains only lowercase English letters