Di Xiao 0005 Longkun Guo Kewen Liao Pei Yao Streaming Submodular Maximization Under Differential Privacy Noise. 431-444 2021 COCOA https://doi.org/10.1007/978-3-030-92681-6_34 conf/cocoa/2021 db/conf/cocoa/cocoa2021.html#XiaoGLY21