codeforces 672C

感觉很简单，就是讨论一下

#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <math.h>
using namespace std;
typedef pair<double,int>pii;
const int N = 1e5+5;
double x[N],y[N];
pii a[N],b[N];
double dis(double x1,double y1,double x2,double y2){
    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
int main(){
    double ax,ay,bx,by,tx,ty,sum=0;
    int n;
    scanf("%lf%lf%lf%lf%lf%lf",&ax,&ay,&bx,&by,&tx,&ty);
    scanf("%d",&n);
    for(int i=1;i<=n;++i)
      scanf("%lf%lf",&x[i],&y[i]);
    for(int i=1;i<=n;++i){
      a[i].second=b[i].second=i;
      double k1=dis(ax,ay,x[i],y[i]);
      double k2=dis(bx,by,x[i],y[i]);
      double k3=dis(tx,ty,x[i],y[i]);
      sum+=k3*2;
      a[i].first=k1-k3;
      b[i].first=k2-k3;
    }
    sort(a+1,a+1+n);
    sort(b+1,b+1+n);
    if(a[1].first>=0&&b[1].first>=0){
        sum+=min(a[1].first,b[1].first);
    }
    else if(a[1].first<0&&b[1].first>=0){
        sum+=a[1].first;
    }
    else if(a[1].first>=0&&b[1].first<0){
        sum+=b[1].first; 
    }
    else {
       if(a[1].second!=b[1].second){
        sum+=a[1].first+b[1].first;
       }
       else {
         if(n==1)sum+=min(a[1].first,b[1].first);
         else {
            double k1=a[1].first+b[2].first;
            double k2=b[1].first+a[2].first;
            k1=min(min(k1,k2),min(a[1].first,b[1].first));
            sum+=k1;
         }
       } 
    }
    printf("%.8f
",sum);    
    return 0;
}