Rabin Karp Algorithm for CompSci369

// RabinKarp counter by Jeremy Lai for CS369 lab2

import java.util.*;
import java.io.*;
import java.math.*;

public class RabinKarp_Jeremy {

    public static final int Q = 121;
    public static final int D = 2;
    public static int TALLY;

    public static void main(String[] args) throws Exception {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String pattern = "";
        String text = "";
        try {
            while (true) {
                pattern = "";
                text = "";
                text = br.readLine();

                if (text == null || text == "" || text.length() <= 0) { throw new Exception(); }

                pattern = br.readLine();

                if (pattern == null || pattern == "" || pattern.length() <= 0) { throw new Exception(); }


                TALLY = 0;

                int position = RabinKarp(pattern, text);

                System.out.println(TALLY);
            }
        }
        catch (Exception e) {
            //e.printStackTrace();
        }

    }

    private static int RabinKarp(String x, String y) {
        int m = x.length();
        int n = y.length();
        long hx = hash(x,0,m);
        long hy = hash(y,0,m);

        for (int j = 0; j <= n - m; ++j) {
            if (hx == hy) {
                //TALLY = 0;
                boolean isEqual = true;
                for (int a = 0; a < m; a++) {
                    TALLY += 1;
                    if (x.charAt(a) != y.charAt(a+j)) {
                        isEqual = false;
                        break;
                    }
                }

                if (isEqual) {
                    return j;
                }
            }
            hy = rehash(y,j,m,hy);

        }
        return -1; // not found
    }

    private static long hash(String str, int from, int m) {
        int power = 0;
        long sum = 0;
        for (int i = from+m-1; i >= from; i--) {
            int charAt = str.charAt(i) - 'a';
            sum += (charAt * power(D, power))%Q;
            power++;
        }
        return sum % Q;
    }

    private static long rehash(String str, int j, int m, long h) {
        try {
            long a = str.charAt(j) - 'a';
            long b = str.charAt(j + m) - 'a';

            long hotchocolate = (a * power(D,m-1)) % Q;
            long sausage = (h - hotchocolate) % Q;
            long bacon = (sausage * D) % Q;
            long eggs = (bacon + b) % Q;

            while (eggs < 0) {
                eggs += Q;
            }

            return eggs % Q;
        }
        catch (Exception e) {  }
        return -1;
    }


    private static long[] CACHE = new long[1000];
    static {
        for (int i = 0; i < CACHE.length; i++) {
            CACHE[i] = power(D, i, true);
        }

    }

    private static long power(int base, int power, boolean b) {
        int total = 1;
        for (int i = 0; i < power; i++) {
            total *= base;
            total %= Q;
        }
        return total;
    }

    private static long power(int base, int power) {
        return CACHE[power];
    }

}