旋转卡壳模版代码

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;
}