问n条平行于x,y的直线交点个数

问n条平行于x,y的直线交点个数
https://onlinejudge.u-aizu.ac.jp/courses/library/4/CGL/6/CGL_6_A

struct Line {
	int st,ed,pos;
	Line() {}
	Line(int a,int b,int c) {
		st=a,ed=b,pos=c;
	}
	bool operator<(const Line&B)const {
		return pos < B.pos;
	}
};
int n;
Point p[N],tmp[N];
vector<Line>vx,vy;

void work() {
	vx.clear(),vy.clear();
	scanf("%d",&n);
	for(int i=0; i<n; i++) {
		double x1,y1,x2,y2;
		scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
		if(x1!=x2) {
			vx.push_back(Line(min(x1,x2),max(x1,x2),y1));
		} else {
			vy.push_back(Line(min(y1,y2),max(y1,y2),x1));
		}
	}
	sort(vy.begin(),vy.end());//根据x排序
	vector<Line>::iterator it;

	int ans =0;
	for(it=vx.begin(); it!=vx.end(); it++) {
		Line now = *it;
		Line s=Line(0,0,now.st);
		Line e=Line(0,0,now.ed+1);
		int l = lower_bound(vy.begin(),vy.end(),s)-vy.begin();
		int r = lower_bound(vy.begin(),vy.end(),e)-vy.begin();
		for(int i=l; i<r; i++) {
			if(vy[i].st<=now.pos && vy[i].ed>=now.pos)ans++;
		}
	}
	printf("%d
",ans);

}