public void push(T x) {
            s_.push(x);
            if(!aux_.isEmpty()) {
                if(x.compareTo(aux_.peek().getFirst()) == 0) {
                    aux_.peek().setSecond(aux_.peek().getSecond() + 1);
                } else if(x.compareTo(aux_.peek().getFirst()) > 0) {
                    aux_.push(new Pair<T, Integer>(x, 1));
                }
            } else {
                aux_.push(new Pair<T, Integer>(x, 1));
            }
        }