1 #include<iostream>
2 #include<cmath>
3 #include<algorithm>
4 using namespace std;
5 #define Max 501
6 double map[Max][Max],d[Max];
7 int n,i,j;
8 struct{
9 int x,y;
10 }point[Max];
11 //记录从顶点集U到V-U的代价最小的边的辅助数组定义
12 struct{
13 int adjvex;
14 double lowcost;
15 }closedge[Max];
16 bool cmp(double a,double b)//从大到小偏序
17 {
18 return a>b;
19 }
20 //用普里姆算法从第k个顶点出发构造网G的最小生产树T
21 void prim(int k)
22 {
23 for(j=1;j<=n;j++)//辅助数组初始化
24 if(j!=k)
25 {
26 closedge[j].adjvex=k;
27 closedge[j].lowcost=map[k][j];
28 }
29 closedge[k].lowcost=0; //初始，U={u}
30 int l=0;
31 for(i=1;i<n;i++)//选择其余n-1个顶点
32 {
33 double min=1000000;
34 for(j=1;j<=n;j++)//求出T的下一个结点：第k顶点
35 if(closedge[j].lowcost!=0&&min>closedge[j].lowcost)
36 {
37 k=j;
38 min=closedge[j].lowcost;
39 }
40 closedge[k].lowcost=0; //第k顶点并入U集
41 d[l++]=map[k][closedge[k].adjvex]; //保存该边
42 for(j=1;j<=n;j++) //新顶点并入U后重新选择最小边
43 if(map[k][j]<closedge[j].lowcost)
44 {
45 closedge[j].adjvex=k;
46 closedge[j].lowcost=map[k][j];
47 }
48 }
49 }
50 int main()
51 {
52 int t,m;
53 cin>>t;
54 while(t--)
55 {
56 cin>>m>>n;
57 for(i=1;i<=n;i++)
58 cin>>point[i].x>>point[i].y;
59 for(i=1;i<=n;i++) //求出毎两个顶点之间的距离
60 for(j=1;j<i;j++)
61 map[i][j]=map[j][i]=sqrt((point[i].x-point[j].x)*(point[i].x
62 -point[j].x)+(point[i].y-point[j].y)*(point[i].y-point[j].y));
63 for(i=1;i<=n;i++)
64 map[i][i]=1000000;
65 prim(1);
66 sort(d,d+n-1,cmp); //把构成最小生成树的n-1条边从大到小排序
67 cout.setf(ios::fixed);//保留两位小数
68 cout.precision(2);
69 cout<<d[m-1]<<endl;//数组d从下标0开始存储，即第m条边
70 }
71 return 0;
72 }
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