code: public Set<Map.Entry<String, Integer>> entrySet()
      {
          Set<Map.Entry<String, Integer>> treeSet = new LinkedHashSet<Map.Entry<String, Integer>>();
          for (Map.Entry<String, Integer> entry : trie.entrySet())
          {
              treeSet.add(new AbstractMap.SimpleEntry<String, Integer>(reverse(entry.getKey()), entry.getValue()));
          }
  
          return treeSet;
      }
docs: 键值对
  @return