[LeetCode] Anagrams

Problem:

Given an array of strings, return all groups of strings that are anagrams.

Note: All inputs will be in lower-case.

Solution:O(n)

public class Solution {
    public ArrayList<String> anagrams(String[] strs) {
        ArrayList<String> list = new ArrayList<String>();
        if(strs == null || strs.length == 0)
            return list;
        HashMap<String,String> map = new HashMap<>();
        for(String s:strs){
            char[] set = s.toCharArray();
            Arrays.sort(set);
            String key = new String(set);
            if(map.get(key)==null){
                map.put(key,s);
            }else{
                if(!list.contains(map.get(key)))
                    list.add(map.get(key));
                list.add(s);
            }
        }
        return list;
    }
}