UVA 11355 Cool Points

view code#include <bits/stdc++.h>

using namespace std;
double PI = acos(-1.0);
int _, cas=1, n, r;

struct event
{
    double x;
    int y;
    bool operator < (const event &o) const{
        return x<o.x;
    }
    event() {}
    event(double x, int y):x(x),y(y) {}
}e[4321];
int ecnt;

void addseg(double a, double b)
{
    if(a>b) swap(a,b);
    e[ecnt++] = event(a, 1);
    e[ecnt++] = event(b, -1);
}

int main()
{
//    freopen("in.txt", "r", stdin);
    cin>>_;
    while(_--)
    {
        scanf("%d%d", &n, &r);
        ecnt = 0;
        double a,b,c,d;
        for(int i=0; i<n; i++)
        {
            scanf("%lf%lf%lf%lf", &a, &b, &c, &d);
            double x = atan2(b,a), y = atan2(d,c);
            if(x<y) swap(x, y);
            if(x-y>PI)
            {
                addseg(-PI, y);
                addseg(x, PI);
            }
            else addseg(x, y);
        }
        int eventnum = 0;
        sort(e, e+ecnt);
        double last = -PI, ans = 0.0;
        for(int i=0; i<ecnt; i++)
        {
            if(eventnum==0)//这里很经典，记下
            {
                ans += e[i].x - last;
            }
            eventnum += e[i].y;
            last = e[i].x;
        }
        ans += PI - last;
        printf("Case %d: %.2f%%\n", cas++, (ans/(PI*2)*100));
    }
    return 0;
}