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