*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:

For the return value, each inner list's elements must follow the lexicographic order.

All inputs will be in lower-case.

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 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());
}
}

reference：https://leetcode.com/discuss/58561/share-my-short-java-solution