package Others;

/** @author Prateek Kumar Oraon (https://github.com/prateekKrOraon) */
import java.util.Scanner;

// An implementation of Rabin-Karp string matching algorithm
// Program will simply end if there is no match
public class RabinKarp {

 public static Scanner scanner = null;
 public static final int d = 256;

 public static void main(String[] args) {

 scanner = new Scanner(System.in);
 System.out.println("Enter String");
 String text = scanner.nextLine();
 System.out.println("Enter pattern");
 String pattern = scanner.nextLine();

 int q = 101;
 searchPat(text, pattern, q);
 }

 private static void searchPat(String text, String pattern, int q) {

 int m = pattern.length();
 int n = text.length();
 int t = 0;
 int p = 0;
 int h = 1;
 int j = 0;
 int i = 0;

 h = (int) Math.pow(d, m - 1) % q;

 for (i = 0; i < m; i++) {
 // hash value is calculated for each character and then added with the hash value of the next
 // character for pattern
 // as well as the text for length equal to the length of pattern
 p = (d * p + pattern.charAt(i)) % q;
 t = (d * t + text.charAt(i)) % q;
 }

 for (i = 0; i <= n - m; i++) {

 // if the calculated hash value of the pattern and text matches then
 // all the characters of the pattern is matched with the text of length equal to length of the
 // pattern
 // if all matches then pattern exist in string
 // if not then the hash value of the first character of the text is subtracted and hash value
 // of the next character after the end
 // of the evaluated characters is added
 if (p == t) {

 // if hash value matches then the individual characters are matched
 for (j = 0; j < m; j++) {

 // if not matched then break out of the loop
 if (text.charAt(i + j) != pattern.charAt(j)) break;
 }

 // if all characters are matched then pattern exist in the string
 if (j == m) {
 System.out.println("Pattern found at index " + i);
 }
 }

 // if i<n-m then hash value of the first character of the text is subtracted and hash value of
 // the next character after the end
 // of the evaluated characters is added to get the hash value of the next window of characters
 // in the text
 if (i < n - m) {
 t = (d * (t - text.charAt(i) * h) + text.charAt(i + m)) % q;

 // if hash value becomes less than zero than q is added to make it positive
 if (t < 0) t = (t + q);
 }
 }
 }
}