Department of Computer Science and Information Engineering, National Taiwan University, Taipei 106, Taiwan. hsiehch@gmail.com|Department of Computer Science and Information Engineering, National Taiwan University, Taipei 106, Taiwan. hsiehch@gmail.com|Department of Computer Science and Information Engineering, National Taiwan University, Taipei 106, Taiwan. hsiehch@gmail.com|Department of Computer Science and Information Engineering, National Taiwan University, Taipei 106, Taiwan. hsiehch@gmail.com|Department of Computer Science and Information Engineering, National Taiwan University, Taipei 106, Taiwan. hsiehch@gmail.com