The aim here is to develop a code in Java for implementing the Rabin-Karp algorithm for matching a string from a set of alphabetical characters that have decimal digits.

Perform the following steps:

1. Convert the text and pattern strings into digits.
2. Use if and for loops to calculate the number of matching characters.
3. Put everything together to implement the Rabin-Karp algorithm. The following Snippet 5.9 shows the pre-compute part of the algorithm:

long q = BigInteger.probablePrime(31, new  Random()).longValue();
// Precompute d^(m-1) % q for use when removing leading digit
long dm = 1;
for (int i = 1; i <= m - 1; i++)
  dm = (d * dm) % q;
// Precompute p and t0
long ph = 0;
long th = 0;
for (int i = 0; i < m; i++) {
  ph = (d * ph + P.charAt(i)) % q;
  th = (d * th + T.charAt(i)) % q;
} 

In the previous implementation, we chose q as a large prime number (using the BigInteger API). We did that so that we have a good hash function and avoided the most of false positives from the p = t_i comparison. This is a similar technique to the one we saw in the remainder method for hash tables in Chapter 3, Hash Tables and Binary Search Trees.