POJ 1113 Wall

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求围墙的长度就是里面凸包的周长+半径为L的圆周长
#include "cstring"#include "iostream"#include "algorithm"#include "cstdio"#include "queue"#include "set"#include "cmath"using namespace std;typedef long long LL;const int M=510;const int INF = 0x3f3f3f3f;const double PI = acos(-1.00);const double EPS = 1e-6;struct point{double x,y;};struct point a[1005],b[1005],p[2005],p1[2005];//p:遍历全部点 p1:记录凸包的点int size;         //凸包点个数bool cmp(point a,point b){//按x从小到大排列；x相同的 按y从小到大排列if(a.x==b.x)return a.y<b.y;return a.x<b.x;}double chaji(point a,point b,point c){return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);}double dist(point a,point b){return sqrt((b.x-a.x)*(b.x-a.x)+(b.y-a.y)*(b.y-a.y));}void sovle(int n){int i;double t;p1[0]=p[0];     //第一个凸包点是第一个点p1[1]=p[1]; //假设..二............二....size=1;    //记录当前假设的凸包点for(i=2;i<n;i++)//遍历所有点{t=chaji(p1[size-1],p1[size],p[i]);//算两个凸包点与该点 向量的叉积while(t<=0)//叉积<=0  该点不是凸包点{size--;if(t==0 || size==0)//垂直 或者凸包点全部遍历完break;t=chaji(p1[size-1],p1[size],p[i]);//直到该点遍历完全部凸包点或者 满足>0为凸包点}p1[++size]=p[i];//记录下一个凸包点}p1[++size]=p[n-2];for(i=n-3;i>=0;i--)//往回找 直到第一个凸包点{t=chaji(p1[size-1],p1[size],p[i]);while(t<=0){size--;if(t==0 || size==0)break;t=chaji(p1[size-1],p1[size],p[i]);}p1[++size]=p[i];}}int main(){int n,i;int l;double sum;while(~scanf("%d%d",&n,&l)){for(i=0;i<n;i++)scanf("%lf%lf",&p[i].x,&p[i].y);sort(p,p+n,cmp);sovle(n);sum=0;for(i=0;i<size;i++)//计算周长sum=sum+dist(p1[i],p1[i+1]);if(size==2)//若只有2个凸包点sum=sum/2;double s=PI*l*2;//printf("%.2lf\n",sum+s+0.5);printf("%d\n",int(sum+s+0.5));}return 0;}
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