public static Map<String, List<String>> buildPrefixLookup (String target, List<String> patterns) {
  Map<String, List<String>> result = new Map<>();
  for (int i = 0; i < target.length(); i++) {
    String s = target.substring(i);
    List<String> list = new List<>();
    for (String pattern : patterns) {
      if (s.startsWith(pattern)) { list.add(pattern); }
    }
    result.initOrBust(s, list);
  }
  return result;
}