rabin-karp

I have generated an string using the following alphabet. {A,C,G,T} . And my string contains more than 10000 characters. I'm searching the following patterns in it. ATGGA TGGAC CCGT I have asked to use a string matching algorithm which has O(m+n) running time. m = pattern length n = text length Both KMP and Rabin-Karp algorithms have this running time. What is the most suitable algorithm (between Rabin-Carp and KMP) in this situation? Ivaylo Strandjev When you want to search for multiple patterns, typically the correct choice is to use Aho-Corasick , which is somewhat a generalization of KMP .

I posed a question to Stackoverflow a few weeks ago about a creating an efficient algorithm to search for a pattern in a large chunk of text. Right now I am using the String function indexOf to do the search. One suggestion was to use Rabin-Karp as an alternative. I wrote a little test program as follows to test an implementation of Rabin-Karp as follows. public static void main(String[] args) { String test = "Mary had a little lamb whose fleece was white as snow"; String p = "was"; long start = Calendar.getInstance().getTimeInMillis(); for (int x = 0; x < 200000; x++) test.indexOf(p); long

I've seen this Rabin Karp string matching algorithm in the forums on the website and I'm interested in trying to implement it but I was wondering If anyone could tell me why the variables ulong Q and ulong D are 100007 and 256 respectively :S? What significance do these values carry with them? static void Main(string[] args) { string A = "String that contains a pattern."; string B = "pattern"; ulong siga = 0; ulong sigb = 0; ulong Q = 100007; ulong D = 256; for (int i = 0; i < B.Length; i++) { siga = (siga * D + (ulong)A[i]) % Q; sigb = (sigb * D + (ulong)B[i]) % Q; } if (siga == sigb) {

According to the wikipedia entry on Rabin-Karp string matching algorithm, it can be used to look for several different patterns in a string at the same time while still maintaining linear complexity. It is clear that this is easily done when all the patterns are of the same length, but I still don't get how we can preserve O(n) complexity when searching for patterns with differing length simultaneously. Can someone please shed some light on this? Edit (December 2011): The wikipedia article has since been updated and no longer claims to match multiple patterns of differing length in O(n). I'm