uva109求凸包面积，判断点是不是在凸包内

#include<map>
#include<set>
#include<cmath>
#include<queue>
#include<stack>
#include<vector>
#include<cstdio>
#include<cassert>
#include<iomanip>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#define pi acos(-1.0)
#define ll long long
#define mod 1000000007
#define ls l,m,rt<<1
#define rs m+1,r,rt<<1|1
#pragma comment(linker, "/STACK:1024000000,1024000000")

using namespace std;

const double g=10.0,eps=1e-7;
const int N=100+10,maxn=500+100,inf=0x3f3f3f;

struct point{
double x,y;
};
point p
,s

;
int n,top
;
bool vis
;
inline bool zero(double x)
{
return fabs(x)<eps;
}
double dis(point p1,point p2)
{
return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}
double dir(point p1,point p2,point p3)
{
return (p3.x-p1.x)*(p2.y-p1.y)-(p3.y-p1.y)*(p2.x-p1.x);
}
bool comp(point p1,point p2)
{
double te=dir(p[0],p1,p2);
if(te<0)return 1;
if(zero(te)&&dis(p[0],p1)<dis(p[0],p2))return 1;
return 0;
}
void Graham(int k)
{
int pos;
double minx=inf,miny=inf;
for(int i=0;i<n;i++)
{
if(p[i].x<minx||(p[i].x==minx&&p[i].y<miny))
{
minx=p[i].x;
miny=p[i].y;
pos=i;
}
}
swap(p[0],p[pos]);
sort(p+1,p+n,comp);
p
=p[0];
s[k][0]=p[0],s[k][1]=p[1], s[k][2]=p[2];
top[k]=2;
for(int i=3;i<=n;i++)
{
while(top[k]>=2&&dir(s[k][top[k]-1],s[k][top[k]],p[i])>=0)top[k]--;
s[k][++top[k]]=p[i];
}
}
double square(int k)
{
double ans=0;
for(int i=0;i<top[k]-1;i++)
ans-=dir(s[k][0],s[k][i],s[k][i+1]);
return ans/2;
}
bool inside(double sq,double x,double y,int k)
{
double ans=0;
point p0;p0.x=x,p0.y=y;
for(int i=0;i<top[k];i++)
{
if(dir(p0,s[k][i],s[k][i+1])<0)ans-=dir(p0,s[k][i],s[k][i+1]);
else ans+=dir(p0,s[k][i],s[k][i+1]);
}
return sq*2==ans;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
int cnt=0;
while(cin>>n,n!=-1){
for(int i=0;i<n;i++)
cin>>p[i].x>>p[i].y;
Graham(cnt);
cnt++;
}
/*  for(int i=0;i<cnt;i++)
{
for(int j=0;j<top[i];j++)
cout<<s[i][j].x<<" "<<s[i][j].y<<endl;
}*/
memset(vis,0,sizeof vis);
int x,y;
double ans=0;
while(cin>>x>>y){
for(int i=0;i<cnt;i++)
{
double sq=square(i);
if(!vis[i]&&inside(sq,x,y,i))
{
vis[i]=1;
ans+=sq;
break;
}
}
}
cout<<setiosflags(ios::fixed)<<setprecision(2)<<ans<<endl;
return 0;
}
/*********************

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