Problem

At Meta, you are given a list of message tokens and need to group together words that are anagrams of each other. Two strings are anagrams if they contain the same characters with the same frequencies, possibly in a different order.

Write a function that takes a list of strings and returns a list of groups, where each group contains strings that are mutual anagrams. The order of groups does not matter, and the order of strings within each group does not matter.

Formal Specification

• Input: strs, a list of lowercase English strings
• Output: A list of lists of strings, where each inner list contains one anagram group

Examples

Example 1

• Input: strs = ["eat", "tea", "tan", "ate", "nat", "bat"]
• Output: [["eat", "tea", "ate"], ["tan", "nat"], ["bat"]]
• Explanation: "eat", "tea", and "ate" share the same sorted form, so they belong in one group.

Example 2

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

Constraints

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