xxxxxxxxxx
public class RabinKarp {
public final static int d = 10;
static void search(String pattern, String str, int q) {
int m = pattern.length();
int n = str.length();
int i, j;
int p = 0;
int t = 0;
int h = 1;
for (i = 0; i < m - 1; i++)
h = (h * d) % q;
// Calculate hash value for pattern and text
for (i = 0; i < m; i++) {
p = (d * p + pattern.charAt(i)) % q;
t = (d * t + str.charAt(i)) % q;
}
// Find the match
for (i = 0; i <= n - m; i++) {
if (p == t) {
for (j = 0; j < m; j++) {
if (str.charAt(i + j) != pattern.charAt(j))
break;
}
if (j == m)
System.out.println("Pattern is found at position: " + (i + 1));
}
if (i < n - m) {
t = (d * (t - str.charAt(i) * h) + str.charAt(i + m)) % q;
if (t < 0)
t = (t + q);
}
}
}
public static void main(String[] args) {
String str = "ABCCDDAEFG";
String pattern = "CDD";
int q = 13;
search(pattern, str, q);
}
}
xxxxxxxxxx
/* Following program is a C implementation of Rabin Karp
Algorithm given in the CLRS book */
#include<stdio.h>
#include<string.h>
// d is the number of characters in the input alphabet
#define d 256
/* pat -> pattern
txt -> text
q -> A prime number
*/
void search(char pat[], char txt[], int q)
{
int M = strlen(pat);
int N = strlen(txt);
int i, j;
int p = 0; // hash value for pattern
int t = 0; // hash value for txt
int h = 1;
// The value of h would be "pow(d, M-1)%q"
for (i = 0; i < M-1; i++)
h = (h*d)%q;
// Calculate the hash value of pattern and first
// window of text
for (i = 0; i < M; i++)
{
p = (d*p + pat[i])%q;
t = (d*t + txt[i])%q;
}
// Slide the pattern over text one by one
for (i = 0; i <= N - M; i++)
{
// Check the hash values of current window of text
// and pattern. If the hash values match then only
// check for characters one by one
if ( p == t )
{
/* Check for characters one by one */
for (j = 0; j < M; j++)
{
if (txt[i+j] != pat[j])
break;
}
// if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]
if (j == M)
printf("Pattern found at index %d \n", i);
}
// Calculate hash value for next window of text: Remove
// leading digit, add trailing digit
if ( i < N-M )
{
t = (d*(t - txt[i]*h) + txt[i+M])%q;
// We might get negative value of t, converting it
// to positive
if (t < 0)
t = (t + q);
}
}
}
/* Driver Code */
int main()
{
char txt[] = "GEEKS FOR GEEKS";
char pat[] = "GEEK";
// A prime number
int q = 101;
// function call
search(pat, txt, q);
return 0;
}