Timefold 中的课程安排连续空白限制策略

2024-03-18 14:20:03

如何限制 Timefold 中课程安排中的连续空白？

引言

在教育环境中，时间表管理是一个复杂的过程，需要考虑多种约束。其中一项关键约束是确保一天内课程安排的连续性，避免课程之间出现较长时间的空白。本文将探讨如何利用 Timefold 的 Timetable Constraint Solver 来实现此约束。

Timefold 中的连续课程限制

Timefold 提供了一个名为 tooMuchGap 的内置约束，它可以防止同一学生组在同一天课程之间出现超过指定时长的空白。此约束使用以下伪代码定义：

foreach pair of different lessons
  with the same student group
  in the same day
  join by start/end times (less than)
  if gap > specified duration
    penalize

限制应用

问题

我们希望对大学一天的课程安排进行限制，确保课程之间的空白时间不超过 2 小时。假设这一天有 7 个时段（8AM - 10AM、10AM - 12AM、...、8PM-10PM）和 4 节不同的课程需要安排。

代码实现

Constraint tooMuchGap(ConstraintFactory constraintFactory){
    // 学生在同一天的课程之间有 4 小时的空档
    //todo 解决这个问题-> 我们接收到的对不是连续的
    return constraintFactory
            //select each 2 pair of different lessons
            .forEach(Lesson.class)
            .join(Lesson.class,
                    //with the same student group
                    Joiners.equal(Lesson::getStudentGroup),
                    //in the same day
                    Joiners.equal((lesson) -> lesson.getTimeslot().getDayOfWeek()),
                    Joiners.lessThan((lesson -> lesson.getTimeslot().getId())))
            .filter((lesson1, lesson2) -> {
                
                Duration between = Duration.between(lesson1.getTimeslot().getEndTime(),
                        lesson2.getTimeslot().getStartTime());
                return !between.isNegative() && between.compareTo(Duration.ofHours(3)) > 0;
            })
            .penalize(HardSoftScore.ONE_SOFT)
            //.justifyWith()
            .asConstraint("Too much gap between the courses");
}

测试验证

@Test
void tooMuchGap(){
    StudentGroup studentGroup = new StudentGroup(1L,"Group1");
    Lesson firstTuesdayLesson = new Lesson(1, "subject1", new Teacher(1L, "Teacher2"), studentGroup, TIMESLOT2, ROOM1);
    Lesson secondTuesdayLesson = new Lesson(2, "subject2", new Teacher(2L, "Teacher1"), studentGroup, TIMESLOT3, ROOM1);
    Lesson thirdTuesdayLesson = new Lesson(3, "subject3", new Teacher(3L, "Teacher3"), studentGroup, TIMESLOT6, ROOM1);
    Lesson fourthTuesdayLesson = new Lesson(4, "subject4", new Teacher(4L, "Teacher3"), studentGroup, TIMESLOT7, ROOM1);
    constraintVerifier.verifyThat(TimetableConstraintProvider::tooMuchGap)
            .given(firstTuesdayLesson, secondTuesdayLesson, thirdTuesdayLesson, fourthTuesdayLesson)
            .penalizesBy(1);
}