public class Solution { public List<List<String>> groupAnagrams(String[] strs) { if(strs==null || strs.length==0) return new ArrayList<List<String>>(); Map<String, List<String>> map = new HashMap<String, List<String>>(); Arrays.sort(strs); for(String str : strs) { char[] cs = str.toCharArray(); Arrays.sort(cs); String keyStr = new String(cs); if(!map.containsKey(keyStr)) map.put(keyStr, new ArrayList<String>()); map.get(keyStr).add(str); } return new ArrayList<List<String>>(map.values()); } }