Group strings that are anagrams

## Problem: Group anagrams Given an array of strings `strs`, group the strings that are anagrams of each other. Two strings are anagrams if they contain the same characters with the same multiplicities (order may differ). ### Input - `strs`: array of strings (assume lowercase English letters unless stated otherwise). ### Output Return a list of groups, where each group is a list of strings that are mutual anagrams. - The order of groups does not matter. - The order of strings inside a group does not matter. ### Constraints (typical) - `1 ≤ len(strs) ≤ 1e5` - `0 ≤ len(strs[i]) ≤ 100` ### Follow-ups discussed in interview - Provide **multiple approaches**, and compare time/space tradeoffs (e.g., sorting-based key vs. character-count key).