Program to implement Rabin Karp algorithm.

                                  In This post we have write a c program to implement implement Rabin Karp algorithm. for subject of Analysis of Algorithms | Computer Engineering | Mumbai University (MU) | (Semester 4) 

Program:

/* 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[] = "Technical Asr Guru";

char pat[] = "Asr Guru";

// A prime number

int q = 101;

// function call

search(pat, txt, q);

return 0;

}

Output: