大致题意：给定一个散点集，求最远点距的平方。
题解：旋转卡壳裸题
代码如下：
1 #include<cstdio> 2 #include<iostream> 3 #include<algorithm> 4 #include<cmath> 5 #define MN 50005 6 using namespace std; 7 int n,top=-1,tmp; 8 double ans; 9 struct point{ 10 double x,y; 11 point(double X=0,double Y=0){x=X,y=Y;} 12 friend bool operator <(point a,point b){ 13 return a.x<b.x||(a.x==b.x&&a.y<b.y); 14 } 15 }p[MN],q[MN]; 16 point operator +(point a,point b){return point(a.x+b.x,a.y+b.y);} 17 point operator -(point a,point b){return point(a.x-b.x,a.y-b.y);} 18 double cross(point a,point b){return a.x*b.y-a.y*b.x;} 19 double len(point a){return a.x*a.x+a.y*a.y;} 20 int main() 21 { 22 scanf("%d",&n); 23 for(int i=1;i<=n;i++) scanf("%lf%lf",&p[i].x,&p[i].y); 24 sort(p+1,p+1+n); 25 for(int i=1;i<=n;i++){ 26 while(top>=1&&cross(q[top]-q[top-1],p[i]-q[top-1])<=0)top--; 27 q[++top]=p[i]; 28 }tmp=top; 29 for(int i=n-1;i>=1;i--){ 30 while(top>tmp&&cross(q[top]-q[top-1],p[i]-q[top-1])<=0)top--; 31 q[++top]=p[i]; 32 } 33 for(int i=0;i<top;i++){ 34 tmp=1; 35 while(cross(q[i+1]-q[i],q[tmp+1]-q[i])>cross(q[i+1]-q[i],q[tmp]-q[i]))tmp=(tmp+1)%top; 36 ans=max(ans,max(len(q[tmp]-q[i]),max(len(q[tmp+1]-q[i]),max(len(q[tmp]-q[i+1]),len(q[tmp+1]-q[i+1]))))); 37 } 38 printf("%.0lf",ans); 39 return 0; 40 }