static L<int> getBracketMap2(L<S> tok, Map<Integer, Integer> map, S openingBrackets, S closingBrackets) {
  map.clear();
  new L<int> stack;
  for (int i = 1; i < l(tok); i+= 2) {
    S t = tok.get(i);
    if (l(t) == 1)
      if (openingBrackets.contains(t))
        stack.add(i);
      else if (closingBrackets.contains(tok.get(i)))
        map.put(empty(stack) ? 0 : liftLast(stack), i);
  }
  ret stack;
}

Began life as a copy of #1002118