Map<Integer, List<Range>> asleepTime =
            shifts.stream()
                  .collect(Collectors.groupingBy(s -> s.getGuard(), Collectors.flatMapping(s -> s.getRanges().stream().filter(r -> r.getState() == State.ASLEEP), Collectors.toList())));

        int asleepMost = asleepTime.entrySet().stream()
                .max(Comparator.comparing(e -> e.getValue().stream().mapToInt(r -> r.getEnd() - r.getStart()).sum()))
                .map(Entry::getKey)
                .get();

        int[] sleepCount = new int[60];
        List<Range> ranges = asleepTime.get(asleepMost);
        for (Range r : ranges) {
            for (int i = r.getStart(); i < r.getEnd(); i++) {
                sleepCount[i]++;
            }
        }

        int maxIdx = -1, max = -1;
        for (int i = 0; i < sleepCount.length; i++) {
            if (sleepCount[i] > max) {
                maxIdx = i;
            }
        }

        int part1 = asleepMost * maxIdx;