POJ1259 The Picnic 最大空凸包问题 DP

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

const int maxn=100;
const double zero=1e-8;
struct Vector
{
 double x,y;	
};

inline Vector operator -(Vector a,Vector b)
{
	Vector c;
	c.x=a.x-b.x;
	c.y=a.y-b.y;
	return c;
}

inline double sqr(double a)
{
 return a*a;
}

inline int Sign(double a)
{
 if(fabs(a)<=zero)return 0;
 return a<0 ? -1:1;
}

inline bool operator <(Vector a,Vector b)
{
 return Sign(b.y-a.y)>0||Sign(b.y-a.y)==0&&Sign(b.x-a.x)>0;

}

inline double Max(double a,double b)
{
 return a>b ? a:b;
}

inline double Length(Vector a)
{
 return sqrt(sqr(a.x)+sqr(a.y));
}

inline double Cross(Vector a,Vector b)
{
 return a.x*b.y-a.y*b.x;
}

Vector dot[maxn],List[maxn];
double opt[maxn][maxn];
int seq[maxn];
int n,len;
double ans;

bool Compare(Vector a,Vector b)
{
 int temp=Sign(Cross(a,b));
 if (temp!=0)return temp>0;
 temp=Sign(Length(b)-Length(a));
 return temp>0;
}

void Solve(int vv)
{
 int t,i,j,_len;
 for(int ii=len=0;ii<n;ii++)
 	{
	 if(dot[vv]<dot[ii])List[len++]=dot[ii]-dot[vv];
	}
 for(i=0;i<len;i++)
 	for(j=0;j<len;j++)
 		opt[i][j]=0;
 sort(List,List+len,Compare);
 double v;
 for(t=1;t<len;t++)
 	{
 	 _len=0;
 	 for(i=t-1;i>=0&&Sign(Cross(List[t],List[i]))==0;i--);
 	 //cout<<i<<endl;
 	 while(i>=0)
 	 	{
 	 	 v=Cross(List[i],List[t])/2.;
 	 	 seq[_len++]=i;
 	 	 for(j=i-1;j>=0&&Sign(Cross(List[i]-List[t],List[j]-List[t]))>0;j--);
 	 	 if(j>=0)v+=opt[i][j];
 	 	 ans=Max(ans,v);
 	 	 opt[t][i]=v;
 	 	 i=j;
		}
	 for(i=_len-2;i>=0;i--)
	    opt[t][seq[i]]=Max(opt[t][seq[i]],opt[t][seq[i+1]]);
	}
}

int i;
double Empty()
{
 ans=0;
 for(i=0;i<n;i++)
 	Solve(i);
 return ans;
}
int main()
{freopen("t.txt","r",stdin);
 int T;
 scanf("%d",&T);
 while(T--)
 	{
 	 scanf("%d",&n);
 	 for(int i=0;i<n;i++)
 	 	scanf("%lf%lf",&dot[i].x,&dot[i].y);
 	 printf("%.1lf\n",Empty());
	}
 return 0;
}