Before revision:  In particular, we first provide a (\frac{1}{2}-\varepsilon) -approximation algorithm that requires O(\frac{1}{\varepsilon} \cdot \log \frac{k}{\varepsilon}) passes over the stream for any constant \varepsilon>0 . In addition, we design a single-pass streaming algorithm that has the same  (\frac{1}{2}-\varepsilon) approximation ratio when unlimited buffer size and post-processing time is permitted\emph{ \emph{ .
After revision:  In particular, we first provide a (\frac{1}{2}-\varepsilon) -approximation algorithm that requires O(\frac{1}{\varepsilon} \cdot \log \frac{k}{\varepsilon}) passes over the stream for any constant \varepsilon>0 . In addition, we design a single-pass streaming algorithm that has the same (\frac{1}{2}-\varepsilon) approximation ratio when unlimited buffer size and post-processing time is permitted\emph{ \emph{personalized recommendation .