Department of Computer Science, National Chiao Tung University, 1001 University Rd,, Hsinchu, Taiwan. yhu@cs.nctu.edu.tw.|Department of Computer Science, National Chiao Tung University, 1001 University Rd,, Hsinchu, Taiwan. yhu@cs.nctu.edu.tw.|Department of Computer Science, National Chiao Tung University, 1001 University Rd,, Hsinchu, Taiwan. yhu@cs.nctu.edu.tw.|Department of Computer Science, National Chiao Tung University, 1001 University Rd,, Hsinchu, Taiwan. yhu@cs.nctu.edu.tw.|Department of Computer Science, National Chiao Tung University, 1001 University Rd,, Hsinchu, Taiwan. yhu@cs.nctu.edu.tw.