1 #include<iostream> 2 #include<cmath> 3 #include<algorithm> 4 #include<cstdio> 5 using namespace std; 6 #define maxn 760 7 int par[maxn]; 8 int n,m; 9 int len;10 int cnt;11 struct node12 {13     int x;14     int y;15     double w;//!!!可以不开方16 };17 node e[maxn * (maxn - 1) / 2];18 int cmp(const node &a , const node &b)19 {20     return a.w < b.w;21 };22 void init()23 {24     for(int i = 1; i <= n+5; i++)25         par[i] = i;26     len = 0;27     cnt = 0;28 }29 int Find(int x)30 {31     int k,j,r;32     r = x;33     while(par[r] != r)34         r = par[r];35     k = x;36     while(k != r)37     {38         j = par[k];39         par[k] = r;40         k = j;41     }42     return r;43 }44 int Merge(int x,int y)45 {46     int a = Find(x);47     int b = Find(y);48     if(a != b)49     {50         par[a] = par[b];51         return 1;52     }53     return 0;54 }55 void input()56 {57     int u,v;58     for(int i = 0; i < n; i++)59         cin>>e[i].x>>e[i].y>>e[i].w;60 }61 62 void make()63 {64     sort(e,e+n,cmp);65     for(int i = 0; i < n; i++)66     {67         if(Merge(e[i].x,e[i].y))68         {69             len += e[i].w;70             cnt++;71         }72 73     }74 }75 int main()76 {77     freopen("input.txt","r",stdin);78     while(cin>>n>>m && n)79     {80         init();81         input();82         make();83         if(cnt < m-1) cout<<"?"<<endl;  //不能单纯n<m-184         else cout<<len<<endl;85     }86 87     return 0;88 }