旋转卡壳模版代码
给定一个平面上的n个点,找出以这些为顶点的三角形,面积最大的一个,输出面积。
#include<stdio.h>
#include<math.h>
#include<algorithm>
using namespace std;
struct Point
{
double x,y;
};
double max(double a,double b)
{
if(a>b)return a;
return b;
}
bool mult(Point curr, Point end, Point begin)
{
return (curr.x-begin.x)*(end.y-begin.y)
>=(end.x-begin.x)*(curr.y-begin.y);
}
bool comp(const Point &a,const Point &b)
{
return a.y<b.y||(a.y==b.y&&a.x<b.x);
}
int graham(Point pnt[], int n, Point res[]) //凸包模版代码
{
int i,len,top=1;
sort(pnt,pnt+n,comp);
if(n==0)
{
return 0;
}
res[0]=pnt[0];
if(n==1)
{
return 1;
}
res[1]=pnt[1];
if(n==2)
{
return 2;
}
res[2]=pnt[2];
for(i=2;i<n;i++)
{
while(top && mult(pnt[i],res[top],res[top-1]))
{
top--;
}
res[++top]=pnt[i];
}
len=top;
res[++top]=pnt[n-2];
for(i=n-3;i>=0;i--)
{
while(len!=top&&mult(pnt[i],res[top],res[top-1]))
{
top--;
}
res[++top]=pnt[i];
}
return top;
}
double Area(Point a,Point b,Point c)
{
return fabs((a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y))/2;
}
int main()
{
Point pnt[400],res[400];
int n;
while(scanf("%d",&n)!=EOF)
{
for(int i=0;i<n;i++)
scanf("%lf%lf",&pnt[i].x,&pnt[i].y);
int top=graham(pnt,n,res);
/*
for(i=0;i<top;i++)
{
printf("%lf %lf\n",res[i].x,res[i].y);
}*/
double ans=0.0;
for(i=0;i<top;i++)
{
int j=(i+1)%top;
int k=(j+1)%top;
while(k!=i && Area(res[i],res[j],res[k])<Area(res[i],res[j],res[(k+1)%top]))
{
k=(k+1)%top;
}
if(k==i)
continue;
int kk=(k+1)%top;
while(j!=kk && k!=i)
{
ans=max(ans,Area(res[i],res[j],res[k]));
while(k!=i && Area(res[i],res[j],res[k])<Area(res[i],res[j],res[(k+1)%top]) )
k=(k+1)%top;
j=(j+1)%top;
}
}
printf("%.2lf\n",ans);
}
return 0;
}