题目：http://acm.hdu.edu.cn/showproblem.php?pid=3932
注意平均值与最远的点距离为0的情况。所以初值设成-1，这样 id 就不会乱。不过设成0也可以。注意判断 pr==0 ，因为有除法。
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #include<ctime> #include<cmath> #include<cstdlib> #define db double using namespace std; const int N=1005; const db dc=0.99,eps=1e-17,INF=2e4; int n,nx[N],ny[N],pid; db ans,px,py; int rdn() { int ret=0;bool fx=1;char ch=getchar(); while(ch>'9'||ch<'0'){if(ch=='-')fx=0;ch=getchar();} while(ch>='0'&&ch<='9') ret=(ret<<3)+(ret<<1)+ch-'0',ch=getchar(); return fx?ret:-ret; } db dis(db x0,db y0,db x1,db y1) { return sqrt((x0-x1)*(x0-x1)+(y0-y1)*(y0-y1)); } void SA(db T) { db x0=px,y0=py,pr=ans;int id=pid; while(T>eps) { pr=0; for(int i=1;i<=n;i++) { db tmp=dis(x0,y0,nx[i],ny[i]); if(tmp>pr)pr=tmp,id=i; } if(pr<ans)ans=pr,pid=id,px=x0,py=y0; if(!pr)return; x0=x0+(nx[id]-x0)/pr*T; y0=y0+(ny[id]-y0)/pr*T; T*=dc; } } int main() { srand(time(0)); int tx,ty; while(scanf("%d%d%d",&tx,&ty,&n)==3) { for(int i=1;i<=n;i++)nx[i]=rdn(),ny[i]=rdn(),px+=nx[i],py+=ny[i]; px/=n; py/=n; ans=INF; SA(10000);SA(10000); printf("(%.1lf,%.1lf). %.1lf ",px,py,ans); } return 0; }