Fast Two-Dimensional Pattern Matching

An algorithm for searching for a two dimensional m m pattern in a two dimensional n n text is presented. It performs on the average less comparisons than the size of the text: n 2 =m using m 2 extra space. Basically, it uses multiple string matching on only n=m rows of the text. It runs in at most 2n 2 time and is close to the optimal n 2 time for many patterns. It steadily extends to an alphabet-independent algorithm with a similar worst case. Experimental results are included for a practical version.