Random primes and Rabin Karp substring search
来源： https://stackoverflow.com/questions/63448730/random-primes-and-rabin-karp-substring-search
rabin-karp
Java indexOf function more efficient than Rabin-Karp? Search Efficiency of Text
问题 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
Need help in understanding Rolling Hash computation in constant time for Rabin-Karp Implementation
问题 I've been trying to implement Rabin-Karp algorithm in Java. I have hard time computing the rolling hash value in constant time. I've found one implementation at http://algs4.cs.princeton.edu/53substring/RabinKarp.java.html. Still I could not get how these two lines work. txtHash = (txtHash + Q - RM*txt.charAt(i-M) % Q) % Q; txtHash = (txtHash*R + txt.charAt(i)) % Q; I looked at couple of articles on modular arithmetic but no article could able to penetrate my thick skull. Please give some
What are the available string matching algorithms besides Knuth-Morris-Pratt, Rabin-Karp and likes of it?
问题 What are the available string matching algorithms besides Knuth-Morris-Pratt, Rabin-Karp and likes of it? 回答1: A well cited compendium of these algorithms can be found in: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.133.4896&rep=rep1&type=pdf Included are the following algorithms: Karp-Rabin Shift Or Morris-Pratt Knuth-Morris-Pratt Simon Colussi Galil-Giancarlo Apostolico-Crochemore Not So Naive Forward Dawg Matching Boyer-Moore Turbo-BM Apostolico-Giancarlo Reverse Colussi
Rabin Karp Algorithm - How is the worst case O(m*n) for the given input?
问题 In the Top Coder's code of RK algorithm: // correctly calculates a mod b even if a < 0 function int_mod(int a, int b) { return (a % b + b) % b; } function Rabin_Karp(text[], pattern[]) { // let n be the size of the text, m the size of the // pattern, B - the base of the numeral system, // and M - a big enough prime number if(n < m) return; // no match is possible // calculate the hash value of the pattern hp = 0; for(i = 0; i < m; i++) hp = int_mod(hp * B + pattern[i], M); // calculate the
Hashing n-grams by cyclic polynomials - java implementation
问题 I'm solving some problem that involves Rabin–Karp string search algorithm. This algorithm requires rolling hash to be faster then naive search. This article describes how to implement rolling hash. I implemented "Rabin-Karp rolling hash" without problems and found few implementations implementations, but article also mentions computational complexity and that hashing n-grams by cyclic polynomials is prefered. It links to BuzHash implementation of such technique but I wonder how it can be used
Hashing n-grams by cyclic polynomials - java implementation
I'm solving some problem that involves Rabin–Karp string search algorithm. This algorithm requires rolling hash to be faster then naive search. This article describes how to implement rolling hash. I implemented "Rabin-Karp rolling hash" without problems and found few implementations implementations , but article also mentions computational complexity and that hashing n-grams by cyclic polynomials is prefered. It links to BuzHash implementation of such technique but I wonder how it can be used to build n-gram hash on top of it. I want to have something like this or CPHash cp = new CPHash(
When to use Rabin-Karp or KMP algorithms?
问题 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? 回答1: When you want to search for multiple patterns,
Are there any working implementations of the rolling hash function used in the Rabin-Karp string search algorithm?
问题 I'm looking to use a rolling hash function so I can take hashes of n-grams of a very large string. For example: "stackoverflow", broken up into 5 grams would be: "stack", "tacko", "ackov", "ckove", "kover", "overf", "verfl", "erflo", "rflow" This is ideal for a rolling hash function because after I calculate the first n-gram hash, the following ones are relatively cheap to calculate because I simply have to drop the first letter of the first hash and add the new last letter of the second hash
Are there any working implementations of the rolling hash function used in the Rabin-Karp string search algorithm?
I'm looking to use a rolling hash function so I can take hashes of n-grams of a very large string. For example: "stackoverflow", broken up into 5 grams would be: "stack", "tacko", "ackov", "ckove", "kover", "overf", "verfl", "erflo", "rflow" This is ideal for a rolling hash function because after I calculate the first n-gram hash, the following ones are relatively cheap to calculate because I simply have to drop the first letter of the first hash and add the new last letter of the second hash. I know that in general this hash function is generated as: H = c 1 a k − 1 + c 2 a k − 2 + c 3 a k −