Counting Distinct Elements in a Data Stream

Ziv Bar-Yossef, T. S. Jayram, Ravi Kumar, D. Sivakumar, Luca Trevisan

Abstract: We present three algorithms to count the number of distinct elements in a data stream to within a factor of 1 ±ε. Our algorithms improve upon known algorithms for this problem, and offer a spectrum of time/space tradeoffs.