HDU ACM 1392 Surround the Trees->凸包

来源：互联网发布：淘宝店推广软文编辑：程序博客网时间：2024/06/10 14:00

分析：直接求出凸包，再算边长即可。另外只有一个点时为0.00单独处理，两个点直接为距离也单独处理。

#include<iostream>#include<cmath>#include<algorithm>using namespace std;struct Point{Point(){}Point(double _x,double _y):x(_x),y(_y){}Point operator-(const Point& a) const{return Point(x-a.x,y-a.y);}double x,y;};double dis(const Point& a,const Point& b){return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}double cross(const Point& a,const Point& b){return a.x*b.y-a.y*b.x;}bool cmp(const Point& a,const Point& b){if(a.x!=b.x)return a.x<b.x;elsereturn a.y<b.y;}int convexhull(Point* p,int n,Point* ch){int i,m,k;sort(p,p+n,cmp);m=0;for(i=0;i<n;i++)   //上凸包{while(m>1 && cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;ch[m++]=p[i];}k=m;for(i=n-2;i>=0;i--) //下凸包{while(m>k && cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;ch[m++]=p[i];}if(n>1) m--;return m;}int main(){Point a[105],p[105];int n,i,m;double ans;while(scanf("%d",&n)==1 &&n){for(i=0;i<n;i++)scanf("%lf%lf",&a[i].x,&a[i].y);if(n==1)printf("0.00\n");else if(n==2){printf("%.2lf\n",dis(a[0],a[1]));}else{m=convexhull(a,n,p);ans=0;for(i=1;i<=m;i++)ans+=dis(p[i],p[i-1]);printf("%.2lf\n",ans);}}return 0;}

0 0