// Group Anagrams — MEDIUM
// Category: string
Given an array of strings `strs`, group the anagrams together. You can return the answer in any order.
Two strings are anagrams if one is a rearrangement of the other's letters.
Example: strs = ["eat","tea","tan","ate","nat","bat"]
Output: [["bat"],["nat","tan"],["ate","eat","tea"]]