public Map<Character, Integer> match_alphabet(String pattern) {
    Map<Character, Integer> s = new HashMap<Character, Integer>();
    char[] char_pattern = pattern.toCharArray();
    for (char c : char_pattern) {
      s.put(c, 0);
    }
    int i = 0;
    for (char c : char_pattern) {
      s.put(c, s.get(c) | (1 << (pattern.length() - i - 1)));
      i++;
    }
    return s;
  }
Initialise the alphabet for the Bitap algorithm.

@param pattern The text to encode.
@return Hash of character locations.
src/burp/Utils/diff_match_patch.java