极角排序

1 #include 
      
        2 #include 
       
         3 #include 
        
          4 #include 
         
           5 #define maxn 30000 6 using namespace std; 7  8 struct point 9 {10     double x,y;11     int num;12 }p[maxn];13 point pp;14 double cross(const point &a,const point &b,const point &c)15 {16     return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);17 }18 bool cmp(const point &a,const point &b)19 {20     if(cross(p[0],a,b)>0) return 0;21     else return 1;22 }23 int main()24 {25     int n;26     int k=0;27     scanf("%d",&n);28     for(int i=0; i