旋转卡壳+一个凸包模板

int ()  
{
    int q=1;
    int ans=0;
    stack[top]=0;//存储凸包点 top为总的点数
    for(int i=0;i<top;i++)
    {
        while( (p[stack[i+1]]-p[stack[i]])*(p[stack[q+1]]-p[stack[i]])>(p[stack[i+1]]-p[stack[i]])*(p[stack[q]]-p[stack[i]]))
            q=(q+1)%(top);
        ans=max(ans , max((p[stack[i]]-p[stack[q]]).len2(),(p[stack[i+1]]-p[stack[q+1]]).len2()));
    }
    return ans;
}