Department of Computer Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China. wjking@hit.edu.cn|Department of Computer Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China. wjking@hit.edu.cn|Department of Computer Science and Engineering, Harbin Institute of Technology, Harbin 150001, PR China. wjking@hit.edu.cn