Pattern matching in pseudo real-timeRaphaël Clifford, Benjamin Sach, Pattern matching in pseudo real-time. CPM'09 special issue of the Journal of Discrete Algorithms, to appear, . September 2010. PDF, 273 Kbytes.
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 Sigma_j Delta(P[j], T[i+j]), where Delta 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.