Sweep Line & Interval

思路:

不需要检测每一时刻,只需要检测起点或者终点的位置!(交点变化的位置只有起点或者终点)
  1. 1.
    将数据拆成二元组 [起点/终点标识,时刻]
  2. 2.
    按照时刻排序
  3. 3.
    依次扫描
...the simple but powerful idea of a sweep line: a vertical line that is conceptually “swept” across the plane. In practice, of course, we cannot simulate all points in time and so we consider only some discrete points.

Template for Point

class Point{
int time;
int flag; // 1=start, 0=end
Point(int time, boolean flag){
this.time = time;
this.flag = flag;
}
public static Comparator<Point> pointComparator = new Comparator<Point>() {
public int compare(Point p1, Point p2){
// 如果时间一致,如果两个都是start或都是end,那么它两相等。如果p1是start而p2是end,那么p1 > p2
if (p1.time == p2.time) return p1.flag - p2.flag;
else return p1.time - p2.time;
}
}

Reference