既好写,又好调
Code:
#include <cstdio> #include <algorithm> #include <cmath> #include <cstring> #define maxn 1000000 #define inf 1000000000000 #define eps 0.0000000000001 #define p point #define setIO(s) freopen(s".in","r",stdin) using namespace std; double tmp=inf,ans; int ck; struct Point{ double x,y; }point[maxn],s[maxn]; double det(double x1,double y1,double x2,double y2){ return x1*y2-x2*y1; } double cross(Point a,Point b,Point c){ return det(b.x-a.x,b.y-a.y,c.x-a.x,c.y-a.y); } double dis(Point a,Point b){ double xx=(a.x-b.x)*1.0, yy=(a.y-b.y)*1.0; xx*=xx,yy*=yy; return (double)sqrt(xx+yy); } int exis(double t) { if(fabs(t) < eps) return 0; else return t > eps ? 1 : -1; } bool cmp(Point a,Point b){ int t=exis(cross(p[1],a,b)); if(t>0) return 1; else if(t<0) return 0; else return dis(p[1],a)<dis(p[1],b); } int main(){ //setIO("input"); int n; scanf("%d",&n); for(int i=1;i<=n;++i) { scanf("%lf%lf",&p[i].x,&p[i].y); if(p[i].y<tmp){ tmp=p[i].y; swap(p[i],p[1]); } } sort(point+2,point+1+n,cmp); s[1]=p[1]; int tot=1; for(int i=2;i<=n;++i) { while(tot>1 && cross(s[tot-1],p[i],s[tot]) >= 0) --tot; ++tot; s[tot]=p[i]; } s[tot+1]=p[1]; for(int i=1;i<=tot;++i) ans+=dis(s[i],s[i+1]); printf("%.2f\n",ans); return 0; }