#### Rabin Karp Algorithm

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```package com.thealgorithms.searches;

// Following program is a Java implementation
// of Rabin Karp Algorithm given in the CLRS book

public class RabinKarpAlgorithm {

// d is the number of characters in the input alphabet
public static final int d = 256;

/* pat -> pattern
txt -> text
q -> A prime number
*/
public int search(String pat, String txt, int q) {
int index = -1; //note: -1 here represent not found, it is not an index
int M = pat.length();
int N = txt.length();
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.charAt(i)) % q;
t = (d * t + txt.charAt(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.charAt(i + j) != pat.charAt(j)) break;
}

// if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]
if (j == M) {
System.out.println("Pattern found at index " + i);
index = i;
return index;
}
}

// Calculate hash value for next window of text: Remove
if (i < N - M) {
t = (d * (t - txt.charAt(i) * h) + txt.charAt(i + M)) % q;

// We might get negative value of t, converting it
// to positive
if (t < 0) t = (t + q);
}
}  