Group Anagrams

Given an array of strings, group anagrams together.

For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"], 
Return:

[
  ["ate", "eat","tea"],
  ["nat","tan"],
  ["bat"]
]

 public class Solution {
     public List<List<String>> groupAnagrams(String[] strs) {
         Map<String, List<String>> map = new HashMap<String, List<String>>();
         for(String str : strs){
             // 将单词按字母排序
             char[] carr = str.toCharArray();
             Arrays.sort(carr);
             String key = new String(carr);
             List<String> list = map.get(key);
             if(list == null){
                 list = new ArrayList<String>();
             }
             list.add(str);
             map.put(key, list);
         }
         List<List<String>> res = new ArrayList<>();
         // 将列表按单词排序
         for(String key : map.keySet()){
             List<String> curr = map.get(key);
             Collections.sort(curr);
             res.add(curr);
         }
         return res;
     }
 }