Действительно по СЛОЖНА, СЛОЖНА
static Set<LocalDateTime> convert(Map<LocalDate, List<LocalTime>> sourceMap) {
Set<LocalDateTime> result = new HashSet<>();
for (Map.Entry<LocalDate, List<LocalTime>> entry : sourceMap.entrySet()) {
for (LocalTime time : entry.getValue()) {
result.add(LocalDateTime.of(entry.getKey(), time));
}
}
return result;