1     public boolean validWordSquare(List<String> words) {
 2         if(words == null || words.size() == 0) {
 3             return false;
 4         }
 5         for(int i = 0; i < words.size(); i++) {
 6             int len = words.get(i).length();
 7             for(int j = 0; j < len; j++) {
 8                 if(words.get(j).length() < i + 1 || words.get(i).length() > words.size() || words.get(j).charAt(i) != words.get(i).charAt(j)) {
 9                     return false;
10                 }
11             }
12         }
13         return true;
14     }