mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
86 lines
2.2 KiB
C++
86 lines
2.2 KiB
C++
#include <iostream>
|
|
#include <cstdio>
|
|
#include <cstring>
|
|
#include <cmath>
|
|
using namespace std;
|
|
const int maxn=1e3+9;
|
|
const double inf=1e11,epx=0.00001;
|
|
int n;
|
|
double rx,ry,d;
|
|
double x[maxn],y[maxn];
|
|
double cal(double x1,double y1,double x2,double y2)
|
|
{
|
|
double a=(x1-x2)*(x1-x2);
|
|
double b=(y1-y2)*(y1-y2);
|
|
return sqrt(a+b);
|
|
}
|
|
bool chk(double xx,double yy)
|
|
{
|
|
for(int i=1;i<=n;i++)
|
|
if(cal(xx,yy,x[i],y[i])>d+epx) return false;
|
|
return true;
|
|
}
|
|
int main()
|
|
{
|
|
while(scanf("%lf %lf",&rx,&ry)!=EOF)
|
|
{
|
|
scanf("%lf",&d);
|
|
scanf("%d",&n);
|
|
for(int i=1;i<=n;i++)
|
|
scanf("%lf %lf",&x[i],&y[i]);
|
|
bool flag=false;
|
|
double ans=inf;
|
|
if(chk(rx,ry))
|
|
{
|
|
ans=0;
|
|
flag=true;
|
|
}
|
|
for(int i=1;i<=n;i++)
|
|
{
|
|
double tmp=cal(x[i],y[i],rx,ry);
|
|
double xx=x[i]+(rx-x[i])*(d/tmp);
|
|
double yy=y[i]+(ry-y[i])*(d/tmp);
|
|
if(ans>cal(xx,yy,rx,ry))
|
|
if(chk(xx,yy))
|
|
{
|
|
ans=cal(xx,yy,rx,ry);
|
|
flag=true;
|
|
}
|
|
}
|
|
for(int i=1;i<=n;i++)
|
|
for(int j=i+1;j<=n;j++)
|
|
{
|
|
if(cal(x[i],y[i],x[j],y[j])>2*d+epx) continue;
|
|
if(fabs(x[i]-x[j])<epx&&fabs(y[i]-y[j])<epx) continue;
|
|
double x1=x[j]-x[i];
|
|
double y1=y[j]-y[i];
|
|
double xx=x[i]+x1/2,yy=y[i]+y1/2;
|
|
double tmp=cal(xx,yy,x[i],y[i]);
|
|
double txt=sqrt(d*d-tmp*tmp);
|
|
double ex,ey;
|
|
if(fabs(x1-0)>epx) ey=1,ex=-y1/x1;
|
|
else ex=1,ey=-x1/y1;
|
|
double tt=sqrt(ex*ex+ey*ey);
|
|
xx+=txt*ex/tt;
|
|
yy+=txt*ey/tt;
|
|
if(cal(xx,yy,rx,ry)<ans)
|
|
if(chk(xx,yy))
|
|
{
|
|
ans=cal(xx,yy,rx,ry);
|
|
flag=true;
|
|
}
|
|
xx-=txt*ex*2/tt;
|
|
yy-=txt*ey*2/tt;
|
|
if(cal(xx,yy,rx,ry)<ans)
|
|
if(chk(xx,yy))
|
|
{
|
|
ans=cal(xx,yy,rx,ry);
|
|
flag=true;
|
|
}
|
|
}
|
|
if(!flag) printf("X\n");
|
|
else printf("%.2lf\n",ans);
|
|
}
|
|
return 0;
|
|
}
|