Solution.java

/**
 * The time complexity of the code is O(n^2), due to the nested stream operation.
 */
class Solution {
  
	@Test
	void test() {
		List<Integer> departures = new ArrayList<>(Arrays.asList(26, 19, 19, 4, 4));
		List<Integer> returns = new ArrayList<>(Arrays.asList(29, 26, 28, 19, 25));

		Collections.sort(departures);
	
		int vansInFleet = 0;
		for(int i = 0; i < departures.size(); i++) {
			int timeDepart = departures.get(i);
			int arrivedThusFar = returns.stream()
                                        .filter(x -> x <= timeDepart)
                                        .collect(Collectors.toList()).size();

			if(vansInFleet + arrivedThusFar <= i) {
				//we don't have a van
				vansInFleet++;
			}

		}
		assertEquals(3, vansInFleet);
	}
}