Shelf Algorithms for Two-Dimensional Packing Problems

This paper studies two approximation algorithms for packing rectangles, using the two-dimensional packing model of Baker, Coffman and Rivest SIAM J. Comput., 9 (1980), pp. 846–855. The algorithms studied are called next-fit and first-fit shelf algorithms, respectively. They differ from previous algorithms by packing the rectangles in the order given; the previous algorithms required sorting the rectangles by decreasing height or width before packing them, which is not possible in some applications. The shelf algorithms are a modification of the next-fit and first-fit decreasing height level algorithms of Coffman, Garey, Johnson and Tarjan SIAM J. Comput., 9 (1980), pp. 808–826. Each shelf algorithm takes a parameter r. It is shown that by choosing r appropriately, the asymptotic worst case performance of the shelf algorithms can be made arbitrarily close to that of the next-fit and first-fit level algorithms, without the restriction that items must be packed in order of decreasing height. Nonasymptotic worst case performance bounds are also investigated.