Group Anagrams

Given an array of strings, group anagrams together.

Example:

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

Note:

• All inputs will be in lowercase.

• The order of your output does not matter.

class Solution {
    public List<List<String>> groupAnagrams(String[] strs) {
        if (strs == null || strs.length == 0)
            return new ArrayList<>();
        Map<String, List<String>> map = new HashMap<>();
        for (String s : strs) {
            char[] arr = new char[26];
            for (char c : s.toCharArray())
                arr[c - 'a']++;
            String key = new String(arr);
            map.computeIfAbsent(key, k -> new ArrayList<>()).add(s);
        }
        return new ArrayList<>(map.values());
    }
}