Pattern matching in pseudo real-time

Abstract

It has recently been shown how to construct online, non-amortised approximate pattern matching algorithms for a class of problems whose distance functions can be classified as being local. Informally, a distance function is said to be local if for a pattern P of length m and any substring T [ i , i + m − 1 ] of a text T, the distance between P and T [ i , i + m − 1 ] can be expressed as ∑ j Δ ( P [ j ] , T [ i + j ] ) , where Δ is any distance function between individual characters. We show in this work how to tackle online approximate matching when the distance function is non-local. We give new solutions which are applicable to a wide variety of matching problems including function and parameterised matching, swap matching, swap-mismatch, k-difference, k-difference with transpositions, overlap matching, edit distance/LCS and L 1 and L 2 rearrangement distances. The resulting online algorithms bound the worst case running time per input character to within a log factor of their comparable offline counterpart.