This is a C Program to implement RabinKarp method. Given a text txt[0..n-1] and a pattern pat[0..m-1], write a function search(char pat[], char txt[]) that prints all occurrences of pat[] in txt[]. You may assume that n > m.
Examples:
1) Input:
txt[] = “THIS IS A TEST TEXT”
pat[] = “TEST”
Output:
Pattern found at index 10
Examples:
1) Input:
txt[] = “THIS IS A TEST TEXT”
pat[] = “TEST”
Output:
Pattern found at index 10
Here is source code of the C Program to Implement Rabin-Karp Method for String Matching. The C program is successfully compiled and run on a Linux system. The program output is also shown below.
#include<stdio.h>
#include<string.h>
// d is the number of characters in 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 on 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 (j == M) // if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]
{
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 program to test above function */
int main()
{
char *txt = "Sanfoundry C Programming Examples";
char *pat = "San";
int q = 101; // A prime number
search(pat, txt, q);
return 0;
}
Output:
$ gcc RabinCarp.c $ ./a.out Pattern found at index 0
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