Department of Computer Science, School of Computer Engineering, Nanyang Technological University, Singapore 639798. sunh0013@e.ntu.edu.sg|Department of Computer Science, School of Computer Engineering, Nanyang Technological University, Singapore 639798. sunh0013@e.ntu.edu.sg|Department of Computer Science, School of Computer Engineering, Nanyang Technological University, Singapore 639798. sunh0013@e.ntu.edu.sg|Department of Computer Science, School of Computer Engineering, Nanyang Technological University, Singapore 639798. sunh0013@e.ntu.edu.sg|Department of Computer Science, School of Computer Engineering, Nanyang Technological University, Singapore 639798. sunh0013@e.ntu.edu.sg