49. 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"]]

Note: All inputs will be in lower-case.

    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 s:strs){            char[] ca = s.toCharArray();            Arrays.sort(ca);            String keyStr = String.valueOf(ca);            if (!map.containsKey(keyStr)) map.put(keyStr, new ArrayList<String>());            map.get(keyStr).add(s);        }        return new ArrayList<List<String>>(map.values());    }

总结：其实有点投机取巧。