hdu3124Arbiter（最小圆距离-扫描线）

链接

详解http://blog.sina.com.cn/s/blog_6e7b12310100qnex.html

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 100000
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 set<int>st;
 struct point
 {
     double x,y,r;
     point(double x = ,double y = ):x(x),y(y){}
     int id;
 }p[N],rank[N];
 struct line
 {
     double po;
     int id;
 }lef[N],rig[N];
 int rk[N],n,pp[N];
 double mid;
 typedef point pointt;
 point operator -(point a,point b)
 {
     return point(a.x-b.x,a.y-b.y);
 }
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     return x<?-:;
 }
 double dis(point a)
 {
     return sqrt(a.x*a.x+a.y*a.y*1.0);
 }
 int is_cross(int a,int b)
 {
     double dd = dis(rank[a]-rank[b]);
     if(dcmp(dd-rank[a].r-rank[b].r-mid-mid)>) return ;
     return ;
 }
 int judge(int a)
 {
     set<int>::iterator it=st.insert(a).first;//插入a后所在位置
     if(it!=st.begin())
     {
         if(is_cross(a,*--it))
         return ;
         it++;
     }
     if(++it!=st.end())
     {
         if(is_cross(a,*it)) return ;
     }
     return ;
 }
 int cal()
 {
     st.clear();
     int i = ,j = ;
     while(i<=n||j<=n)
     {
         if(j==n+||(i!=n+&&dcmp(lef[i].po-mid-(rig[j].po+mid))<=))//如果当且i圆的最左端小于j圆的最右端 将i插进来
         {
             int ip = rk[lef[i].id];
             if(judge(ip))
             return ;
             i++;
         }
         else
         {
             st.erase(rk[rig[j].id]);
             j++;
         }
     }
     return ;
 }
 double solve()
 {
     double low = 0.0,high = dis(p[]-p[])-p[].r-p[].r;
     while(low+eps<high)//二分距离
     {
         mid = (high+low)/;
         if(cal())
         high = mid;
         else low = mid;
     }
     return high+low;
 }
 bool cmp(line a,line b)
 {
     return a.po<b.po;
 }
 bool cmpp(point a,point b)
 {
     if(a.y==b.y) return a.x<b.x;
     return a.y<b.y;
 }
 int main()
 {
     int t,i;
     cin>>t;
     while(t--)
     {
         scanf("%d",&n);
         for(i = ; i <=n ;i++)
         {
             scanf("%lf%lf%lf",&p[i].x,&p[i].y,&p[i].r);
             lef[i].po = p[i].x-p[i].r;//每个圆的最左端
             lef[i].id = i;
             rig[i].po = p[i].x+p[i].r;//每个圆的最右端
             rig[i].id = i;
             rank[i] = p[i];//按y坐标排序
             rank[i].id = i;
         }
         sort(lef+,lef+n+,cmp);
         sort(rig+,rig+n+,cmp);
         sort(rank+,rank+n+,cmpp);
         for(i = ; i <= n; i++)
         {
             rk[rank[i].id] = i;//每个圆按y坐标排序后位于第几
         }
         double ans = solve();
         printf("%.6f\n",ans);
     }
     return ;
 }