poj1113 Wall
题目描述:
题解:
答案就是凸包周长+2πL。
代码:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include<cmath> #include<cstdio> #include<vector> #include<cstring> #include<algorithm> using namespace std; const int N = 1050; const double Pi = acos(-1.0); struct Point { double x,y; Point(){} Point(double x,double y):x(x),y(y){} Point operator + (const Point&a)const{return Point(x+a.x,y+a.y);} Point operator - (const Point&a)const{return Point(x-a.x,y-a.y);} double operator * (const Point&a)const{return x*a.x+y*a.y;} double operator ^ (const Point&a)const{return x*a.y-y*a.x;} bool operator < (const Point&a)const{return x!=a.x?x<a.x:y<a.y;} }; typedef Point Vector; int n; double L; Point p[N],s[N]; double lth(const Vector&a){return sqrt(a*a);} int build() { sort(p+1,p+1+n); int tl = 0; for(int i=1;i<=n;i++) { while(tl>1&&((s[tl]-s[tl-1])^(p[i]-s[tl-1]))<=0)tl--; s[++tl]=p[i]; } int k = tl; for(int i=n-1;i>=1;i--) { while(tl>k&&((s[tl]-s[tl-1])^(p[i]-s[tl-1]))<=0)tl--; s[++tl]=p[i]; } if(tl!=1)tl--; return tl; } int main() { scanf("%d%lf",&n,&L); for(int i=1;i<=n;i++) scanf("%lf%lf",&p[i].x,&p[i].y); int m = build(); double ans=0.0; for(int i=1;i<m;i++) ans+=lth(s[i+1]-s[i]); ans+=lth(s[1]-s[m]); printf("%.0lf\n",ans+Pi*L*2); return 0; }