public static int rabinKarp(String text, String pattern) {
        //Doing Double Hashing for cross-checking. Choose any 2 MOD and BASE which are primes.
        long MOD1 = (int) Math.pow(10,9)+7;
        long BASE1 = 101;
        long MOD2 = 2* (int) Math.pow(10,9) + 11;
        long BASE2 = 301;
        int n = text.length() , m = pattern.length(), i;
        if(n<m) return -1;
        //compute HashCode for the pattern
        long hashPattern1=0, hashPattern2=0;
        for(i = m-1; i >= 0; i--) {
            hashPattern1 = (hashPattern1 + pattern.charAt(i) * BASE1)% MOD1;
            hashPattern2 = (hashPattern2 + pattern.charAt(i) * BASE2)% MOD2;
        }
        long hashText1 =0 , hashText2 = 0;
        //compute hashCodes of the first M chars.
        for(i=0;i<m;i++) {
            hashText1 *= BASE1;
            hashText2 *= BASE2;
            hashText1 = (hashText1 + text.charAt(i))% MOD1;
            hashText2 = (hashText2 + text.charAt(i))% MOD2;
        }
        if(hashPattern1 == hashText1 && hashPattern2 == hashText2) return 0;
        for(i=m;i<n;i++) {
            hashText1 *= BASE1;
            hashText2 *= BASE2;
            hashText1 = (hashText1 + text.charAt(i))% MOD1;
            hashText2 = (hashText2 + text.charAt(i))% MOD2;
            if(hashPattern1 == hashText1 && hashPattern2 == hashText2) {
                // additionally verify that the text actually matches,  can be done
                /*
                for(int j=0;j<m;j++)
                    if(text.charAt(i+j) != pattern.charAt(j))
                        break;
                if(j==m) return i;
                 */
                return i;
            }
        }
        return -1;
    }