1. School of Automation Science and Electrical Engineering, University of Science and Technology Beijing, Beijing, China
2. Intelligent Recommendation Group of Search Division, Technology Center of Qihoo 360 Technology Company Ltd., Beijing, China
3. Computing and Network Research Department, Research Institute of China Unicom, Beijing, China
4. School of Artificial Intelligence, Beijing University of Posts and Telecommunications, Beijing, China
5. Beijing Key Laboratory of Mobile Computing and Pervasive Device, Institute of Computing Technology, Chinese Academy of Sciences, Beijing, China