A faster and simpler 2-approximation algorithm for block sorting

Abstract

Block sorting is used in connection with optical character recognition (OCR). Recent work has focused on finding good strategies which perform well in practice. Block sorting is NP-hard and all of the previously known heuristics lack proof of any approximation ratio. We present here an approximation algorithm for the block sorting problem with approximation ratio of 2 and run time O(n2). The approximation algorithm is based on finding an optimal sequence of absolute block deletions. © Springer-Verlag Berlin Heidelberg 2005.