求凸包模版

struct point{ double x,y; double val,len; }points[20]; point points1[20]; point points2[20]; const int INF=1e8; bool cmp(point a,point b) { if(a.x==b.x) return a.y
     
      1&&chaji(points2[ansnum-2],points2[ansnum-1],points2[ansnum-1],points1[i])<0) ansnum--; points2[ansnum++]=points1[i]; } int k=ansnum; for(int i=potnum-2;i>=0;i--) { while(ansnum>k&&chaji(points2[ansnum-2],points2[ansnum-1],points2[ansnum-1],points1[i])<0) ansnum--; points2[ansnum++]=points1[i]; } if(potnum>1) ansnum--; return ansnum; } double way(point a,point b) { return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); }