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<>();
    Map<String,List<String>> map = new HashMap<>();//map存的是String和String的List
    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<>());
        map.get(keyStr).add(s);
    }
    return new ArrayList<>(map.values());
}