Department of Computer Science, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, HsinChu, 30013, Taiwan. tychiu@vc.cs.nthu.edu.tw.|Department of Computer Science, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, HsinChu, 30013, Taiwan. tchsu@vc.cs.nthu.edu.tw.|Department of Computer Science, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, HsinChu, 30013, Taiwan. ccyen@vc.cs.nthu.edu.tw.|Department of Computer Science, National Tsing Hua University, No. 101, Section 2, Kuang-Fu Road, HsinChu, 30013, Taiwan. jswang@cs.nthu.edu.tw.