[lintcode medium]Anagrams

public class Solution {
    /**
     * @param strs: A list of strings
     * @return: A list of strings
     */
    public List<String> anagrams(String[] strs) {
        // write your code here
        
        List<String> list=new ArrayList<String>();
        if(strs==null ||strs.length==0) return list;
        HashMap<String,Integer> visited=new HashMap<String,Integer>();
        for(int i=0;i<strs.length;i++)
        {
            char[] ch=strs[i].toCharArray();
            Arrays.sort(ch);
            String s=new String(ch);
            
            if(visited.containsKey(s))
            {
                int index=visited.get(s);
                if(index!=-1)
                {
                    list.add(strs[index]);
                    visited.put(s,-1);
                }
                list.add(strs[i]);
            }
            else
            {
                visited.put(s,i);
            }
        }
        return list;
    }
}