https://blog.csdn.net/linkfqy/article/details/72861176
#include<iostream> #include<cmath> #include<algorithm> #define N 10005 #define eps 1e-6 using namespace std; int n; struct Point { double x,y; Point(double x=0,double y=0):x(x),y(y){} }p[N]; typedef Point Vector; Vector operator +(Point a,Vector b) { return Point(a.x+b.x,a.y+b.y); } Vector operator -(Point a,Point b) { return Point(a.x-b.x,a.y-b.y); } Vector operator *(Vector a,double k) { return Point(a.x*k,a.y*k); } double Dot(Vector a,Vector b) { return (a.x*b.x)+(a.y*b.y); } double Cross(Vector a,Vector b) { return (a.x*b.y)-(a.y*b.x); } double Len(Vector a) { return sqrt(Dot(a,a)); } inline bool cmp(const Point &a,const Point &b) { if(fabs(a.x-b.x)>eps) return a.x<b.x; else return a.y<b.y; } int sta[N]; void Andrew() { sta[1]=1; int top=1; for(int i=2;i<=n;i++) { while(top>1&&(Cross(p[i]-p[sta[top-1]],p[sta[top]]-p[sta[top-1]])<eps)) top--; sta[++top]=i; } int k=top; for(int i=n-1;i>=1;i--) { while(top>k&&(Cross(p[i]-p[sta[top-1]],p[sta[top]]-p[sta[top-1]])<eps)) top--; sta[++top]=i; } double ans=0; for(int i=1;i<top;i++) { ans+=Cross(p[sta[i]]-p[sta[1]],p[sta[i+1]]-p[1]); } cout<<abs(int(ans/100))<<endl; } int main() { cin>>n; for(int i=1;i<=n;i++) { cin>>p[i].x>>p[i].y; } sort(p+1,p+n+1,cmp); Andrew(); return 0; }转载于:https://www.cnblogs.com/Patrickpwq/articles/9808850.html
