An Index for Two Dimensional String Matching Allowing Rotations

We present an index to search a two-dimensional pattern of size m m in a two-dimensional text of size n n, even when the pattern appears rotated in the text. The index is based on (path compressed) tries. By using O(n2 ) (i.e. linear) space the index can search the pattern in O((log n)5=2 ) time on average, where is the alphabet size. We also consider various schemes for approximate matching, for which we obtain either O(polylog n) or O(n2 ) search time, where < 1 in most useful cases. A larger index of size O(n2 (log n)3=2 ) yields an average time of O(log n) for the simplest matching model. The algorithms have applications e.g. in content based information retrieval from image databases.

• Type: Conference
• Year: 2000
• Where: IFIPTCS
• Authors: Kimmo Fredriksson, Gonzalo Navarro, Esko Ukkonen
• Keywords: Alphabet Size, IFIPTCS 2000, Theoretical Computer Science, Two-dimensional Pattern, Two-dimensional Text