Packing a bin on-line to maximize the total number of items

A bin of capacity 1 and a finite sequence σ of items of sizes a1,a2,… are considered, where the items are given one by one without information about the future. An online algorithm A must irrevocably decide whether or not to put an item into the bin whenever it is presented. The goal is to maximize the number of items collected. A is f-competitive for some function f if n*(σ) ≤ f(nA(σ)) holds for all sequences σ, where n* is the (theoretical) optimum and nA the number of items collected by A. A necessary condition on f for the existence of an f-competitive (possibly randomized) online algorithm is given. On the other hand, this condition is seen to guarantee the existence of a deterministic online algorithm that is “almost” f-competitive in a well-defined sense