Department of Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan. yclin@cse.nsysu.edu.tw|Department of Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan. yclin@cse.nsysu.edu.tw|Department of Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan. yclin@cse.nsysu.edu.tw