49. 字母异位词分组

    public List<List<String>> groupAnagrams(String[] strs) {
        HashMap<String, List<String>> map = new HashMap<String, List<String>>();
        for (String str : strs) {
            char[] chars = str.toCharArray();
            // 排序后的字符串相等
            Arrays.sort(chars);
            String key = String.valueOf(chars);
            List<String> list = map.getOrDefault(key, new ArrayList<String>());
            list.add(str);
            map.put(key, list);
        }
        return new ArrayList<>(map.values());
    }