Approximation Algorithms for Rectangle Packing Problems (PhD Thesis)

TL;DR

This thesis develops improved approximation algorithms for various rectangle packing problems, introducing a container-based framework and novel techniques to surpass previous approximation barriers, especially for 2DGK with and without rotations.

Contribution

It presents a unified container-based framework for rectangle packing problems, achieving better approximation ratios and breaking the 2-approximation barrier for certain variants.

Findings

Improved pseudo-polynomial time approximation for strip packing.

First algorithms with approximation factor better than 2 for 2D knapsack with rotations.

Breaks the 2-approximation barrier for a generalized packing problem.

Abstract

In rectangle packing problems we are given the task of placing axis-aligned rectangles in a given plane region, so that they do not overlap with each other. In Maximum Weight Independent Set of Rectangles (MWISR), their position is given and we can only select which rectangles to choose, while trying to maximize their total weight. In Strip Packing (SP), we have to pack all the given rectangles in a rectangular region of fixed width, while minimizing its height. In 2-Dimensional Geometric Knapsack (2DGK), the target region is a square of a given size, and our goal is to select and pack a subset of the given rectangles of maximum weight. We study a generalization of MWISR and use it to improve the approximation for a resource allocation problem called bagUFP. We revisit some classical results on SP and 2DGK, by proposing a framework based on smaller containers that are packed with simpler rules; while variations of this scheme are indeed a standard technique in this area, we abstract away some of the problem-specific differences, obtaining simpler algorithms that work for different problems. We obtain improved approximations for SP in pseudo-polynomial time, and for a variant of 2DGK where one can to rotate the rectangles by 90{\deg}. For the latter, we propose the first algorithms with approximation factor better than 2. For the main variant of 2DGK (without rotations), a container-based approach seems to face a natural barrier of 2 in the approximation factor. Thus, we consider a generalized kind of packing that combines container packings with another packing problem that we call L-packing problem, where we have to pack rectangles in an L-shaped region of the plane. By finding a (1 + {\epsilon})-approximation for this problem and exploiting the combinatorial structure of 2DGK, we obtain the first algorithms that break the barrier of 2 for the approximation factor of this problem.