向总让我们买的数学书还挺好的啊。。有凸包模板程序蒯。。
于是蒯了一遍，改了改。。还挺爽的
以前自己打的时候各种直线垂直什么的特判到死。。写这个题只有40分。。
蒯永远是很爽的！
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// <Graham.cpp> - 03/29/16 15:06:36 // This file is created by XuYike's black technology automatically. // Copyright (C) 2015 ChangJun High School, Inc. // I don't know what this program is. #include <iostream> #include <vector> #include <algorithm> #include <cstring> #include <cstdio> #include <cmath> using namespace std; typedef long long lol; int getint(){ int res=0,fh=1;char ch=getchar(); while((ch>'9'||ch<'0')&&ch!='-')ch=getchar(); if(ch=='-')fh=-1,ch=getchar(); while(ch>='0'&&ch<='9')res=res*10+ch-'0',ch=getchar(); return fh*res; } #define f(x) ((x)*(x)) const int MAXN=100002; int n,X,Y; struct point{ int x,y; bool operator <(const point b) const{ int v1x=x-X,v1y=y-Y,v2x=b.x-X,v2y=b.y-Y; int j=v1x*v2y-v2x*v1y; return !j?x>=b.x:j<0; } }p[MAXN]; int s[MAXN]; int main(){ freopen("Graham.in","r",stdin); freopen("Graham.out","w",stdout); n=getint(); for(int i=0;i<n;i++)p[i].x=getint(),p[i].y=getint(); int l=0; for(int i=1;i<n;i++)if(p[i].x<p[l].x||(p[i].x==p[l].x&&p[i].y<p[l].y))l=i; swap(p[0],p[l]); X=p[0].x,Y=p[0].y; sort(p+1,p+n); p[n]=p[0]; int top=2; s[1]=0;s[2]=1; for(int i=2;i<=n;i++){ while(top>1){ int v1x=p[s[top]].x-p[s[top-1]].x,v1y=p[s[top]].y-p[s[top-1]].y, v2x=p[i].x-p[s[top]].x,v2y=p[i].y-p[s[top]].y; if(v1x*v2y-v2x*v1y<0)break; top--; } s[++top]=i; } double ans=0; for(int i=2;i<=top;i++) ans+=sqrt(double(f(p[s[i]].x-p[s[i-1]].x)+f(p[s[i]].y-p[s[i-1]].y))); printf("%.1lf",ans); return 0; } |
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