Rabin-Karp.c

#include<stdio.h>
#include<string.h>

#define d 256

void search(char pat[], char txt[], int q)
{
	int M = strlen(pat);
	int N = strlen(txt);
	int i, j;
	int p = 0; 
	int t = 0; 
	int h = 1;

	
	for (i = 0; i < M-1; i++)
		h = (h*d)%q;


	for (i = 0; i < M; i++)
	{
		p = (d*p + pat[i])%q;
		t = (d*t + txt[i])%q;
	}

	
	for (i = 0; i <= N - M; i++)
	{

		
		if ( p == t )
		{
			
			for (j = 0; j < M; j++)
			{
				if (txt[i+j] != pat[j])
					break;
			}

			
			if (j == M)
				printf("Pattern found at index %d \n", i);
		}

		
		if ( i < N-M )
		{
			t = (d*(t - txt[i]*h) + txt[i+M])%q;

			
			if (t < 0)
			t = (t + q);
		}
	}
}


int main()
{
	char txt[] = "GEEKS FOR GEEKS";
	char pat[] = "GEEK";

	
	int q = 101; 

	search(pat, txt, q);
	return 0;
}