P2742 【模板】二維凸包 / [USACO5.1]圈奶牛Fencing the Cows
阿新 • • 發佈:2018-11-20
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//minamoto #include<bits/stdc++.h> #define rint register int #define inf 0x3f3f3f3f using namespace std; const int N=10005; struct node{ double x,y; node(){} node(double x,double y):x(x),y(y){} inline bool operator <(const node &b)const{ double A=atan2((a.y-p[1].y),(a.x-p[1].x)); double B=atan2((b.y-p[1].y),(b.x-p[1].x)); return A!=B?A<B:a.x<b.x; } }p[N],st[N]; int n,k,top;double ans; inline bool cmp(node a,node b){ double A=atan2((a.y-p[1].y),(a.x-p[1].x)); double B=atan2((b.y-p[1].y),(b.x-p[1].x)); return A!=B?A<B:a.x<b.x; } inline double cross(node a,node b,node c){return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);} inline double dis(node a,node b){return sqrt((b.y-a.y)*(b.y-a.y)+(b.x-a.x)*(b.x-a.x));} int main(){ // freopen("testdata.in","r",stdin); scanf("%d",&n),p[0]={inf,inf}; for(rint i=1;i<=n;++i){ scanf("%lf%lf",&p[i].x,&p[i].y); if(p[0].y>p[i].y||(p[0].y==p[i].y&&p[i].x<p[0].x))p[0]=p[i],k=i; } swap(p[k],p[1]),sort(p+2,p+n+1,cmp); st[0]=p[1],st[1]=p[2],top=1; for(rint i=3;i<=n;++i){ while(top&&cross(st[top-1],p[i],st[top])>=0)--top; st[++top]=p[i]; } st[top+1]=p[1];for(rint i=0;i<=top;++i)ans+=dis(st[i],st[i+1]); printf("%.2lf\n",ans);return 0; }
P2742 【模板】二維凸包 / [USACO5.1]圈奶牛Fencing the Cows