public List<List<String>> groupAnagrams(String[] strs) {
List<List<String>> res = new ArrayList<>();
if (strs == null || strs.length == 0) {
Map<String, List<String>> map = new HashMap<>();
for (String str : strs) {
int[] count = new int[256];
for (char c : str.toCharArray()) {
StringBuilder key = new StringBuilder();
for (char c = 0; c < 256; c++) {
map.putIfAbsent(key.toString(), new ArrayList<>());
map.get(key.toString()).add(str);
for (String key : map.keySet()) {