sort.java

private static boolean hasSortedBlocks(Iterable<Double> iterable, Comparator comparator) {
        Iterator<Double> it = iterable.iterator();
        if (it.hasNext()) {
            Double prev = it.next();
            Double next;
            Double secondNext = null;
            Double thirdNext = null;
            while (it.hasNext()) {
                next = it.next();
                if (compare(comparator, prev, next) && it.hasNext()) {
                    secondNext = it.next();
                    if (compare(comparator, next, secondNext) && it.hasNext()) {
                        thirdNext = it.next();
                        if (compare(comparator, secondNext, thirdNext)) {
                            return false;
                        }
                    }
                }
                if (thirdNext != null) {
                    prev = thirdNext;
                } else if (secondNext != null) {
                    prev = secondNext;
                } else {
                    prev = next;
                }
            }
        }
        return true;
    }