A COMBINED BIT AND TIMESTAMP ALGORITHM FOR THE LIST UPDATE PROBLEM

We present a randomized on-line algorithm for the list update problem which achieves a competitive factor of 1.6, the best known so far. The algorithm makes an initial random choice between two known algorithms that have different worst-case request sequences. The first is the BI T algorithm that, for each item in the list, alternates between moving it to the front of the list and leaving it at its place after it has been requested. The second is a TIMESTAMP algorithm that moves an item in front of less often requested items within the list.