UVALive 6324 Archery （求射箭覆盖的期望）

#include<cstdio>

#include<cmath>

#include<cstring>

#include<cstdlib>

const double pi=3.141592653;

int main(){

  int t;

  scanf("%d",&t);

  while(t--){

    int n;

    scanf("%d",&n);

    double ans=;

    double x1,y1,x2,y2;

    for(int i=;i<=n;i++){

        scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);

        double temp=fabs(atan2(y1,x1)-atan2(y2,x2));//atan2，特别注意

        if(temp>pi)

            temp=2.0*pi-temp;

            ans+=temp;

        }

      printf("%.5lf\n",ans/(pi*2.0));

  }

  return ;

}