POJ 3348 最直接的凸包问题

题目大意：

给定一堆树的点，找到能组合成的最大面积，一个物体占50面积，求最多放多少物体

 #include <cstdio>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 using namespace std;
 const double eps = 1e-;
 const int N = ;
 double myabs(double x)
 {
     return x>?x:-x;
 }
 struct Point{
     double x,y;
     Point(double x= , double y=):x(x),y(y){}
 };
 Point p[N] , ch[N];
 typedef Point Vector;
 Vector operator+(Vector a , Vector b){
     return Vector(a.x + b.x , a.y + b.y);
 }
 Vector operator-(Point a , Point b){
     return Vector(a.x - b.x , a.y - b.y);
 }
 Vector operator*(Vector a, double b){
     return Vector(a.x*b , a.y*b);
 }
 Vector operator/(Vector a, double b){
     return Vector(a.x / b , a.y/b);
 }
 int dcmp(double x){
     if(myabs(x) < eps) return ;
     return x<?-:;
 }
 bool operator==(Point a ,Point b){
     return dcmp(a.x-b.x) ==  && dcmp(a.y-b.y) == ;
 }
 bool operator<( Point a , Point b){
     return dcmp(a.x-b.x)< || (dcmp(a.x-b.x)== && dcmp(a.y-b.y)<);
 }
 double Cross(Vector a , Vector b){
     return a.x*b.y - b.x*a.y;
 }
 double get_polexy_area(Point *p , int n){
     double ans = ;
     for(int i=;i<n-;i++){
         ans += Cross(p[i] - p[] , p[i+] - p[]);
     }
     return ans / ;
 }
 int ConvexHull(Point *p, int n) //凸包
 {
     sort(p, p+n);
     n = unique(p, p+n) - p; //去重
     int m = ;
     for(int i = ; i < n; i++)
     {
         while(m >  && Cross(ch[m-]-ch[m-], p[i]-ch[m-]) <= ) m--;
         ch[m++] = p[i];
     }
     int k = m;
     for(int i = n-; i >= ; i--)
     {
         while(m > k && Cross(ch[m-]-ch[m-], p[i]-ch[m-]) <= ) m--;
         ch[m++] = p[i];
     }
     if(n > ) m--;
     return m;
 }
 int main()
 {
     //freopen("test.in","rb",stdin);
     int n;
     while(~scanf("%d",&n)){
         for(int i=;i<n;i++){
             scanf("%lf%lf" , &p[i].x , &p[i].y);
         }
         int m = ConvexHull(p,n);
         double area = get_polexy_area(ch , m);
         int ans = (int)(area/);
         printf("%d\n",ans);
     }
     return ;
 }