[1] Ant Grp, SCI Lab, Hangzhou, Peoples R China
[2] Stanford Univ, Dept CS, Stanford, CA 94305 USA
[3] Zhejiang Univ, Coll CST, Hangzhou, Peoples R China
[4] Univ Calif Berkeley, Dept EECS, Berkeley, CA USA
[5] Texas A&M Univ, Dept CSE, College Stn, TX 77843 USA