Finding frequent items over sliding windows with constant update time

a r t i c l e i n f o a b s t r a c t In this paper, we consider the problem of finding-approximate frequent items over a sliding window of size N. A recent work by Lee and Ting (2006) [7] solves the problem by giving an algorithm that supports O (1) query and update time, and uses O (1) space. Their query time and memory usage are essentially optimal, but the update time is not. We give a new algorithm that supports O (1) update time with high probability while maintaining the query time and memory usage as O (1).