判断一个无向连通图的MST是否唯一，其实本质上就是求是否存在次小树恰好等于MST。
   16ms碾过~ 数据弱，不建议用来测试模版，据说有非SST做法，kuskal + LCA + O(E) ？求大神教学……

 1 /*
 2 Problem: 1679        User: _mTy
  3 Memory: 760K        Time: 16MS
  4 Language: G++        Result: Accepted
  5
 6 Source Code
  7 */
 8
 9 # include<cstdio>
10 # include<cstdlib>
11 # include<cstring>
12 # include<queue>
13 # define N 101
14 using namespace std;
 15
16 struct nod{
 17     int u , max ;
 18 };
 19 int g[N][N];
 20 int tree[N][N];
 21 int best[N][N];
 22
23 int prim(int n , int fa[]);
 24
25 int main(){
 26     int t , n , m;
 27     int i , j , u , v , w , t1 , total;
 28     int fa[N];
 29     struct nod tmp , arr[N * N];
 30     bool unique , visi[N];
 31     scanf( " %d " ,& t);
 32      while (t -- ){
 33         scanf( " %d%d " ,& n ,& m);
 34          for (i = 0 ;i < n;i ++ )  for (j = 0 ;j < n;j ++ ) g[i][j] = 0x7fffffff ;
 35         memset(tree ,- 1 , sizeof (tree));
 36          for (i = 0 ;i < m;i ++ ){
 37             scanf( " %d%d%d " ,& u ,& v ,& w);
 38             g[u - 1 ][v - 1 ] = g[v - 1 ][u - 1 ] = w;
 39         }
 40         t1 = prim(n , fa);
 41          for (i = 0 ;i < n;i ++ ) tree[i][fa[i]] = tree[fa[i]][i] = g[i][fa[i]];
 42
43          //  bfs
44         total = 0 ;
 45         memset(best ,- 1 , sizeof (best));
 46          for (i = 0 ;i < n;i ++ ){
 47             memset(visi , 0 , sizeof (visi));
 48             arr[total] . u = i; arr[total] . max =- 1 ;
 49             queue < struct nod >  _que; _que . push(arr[total]);  ++ total;
 50             visi[i] = 1 ;
 51              while ( ! _que . empty ()){
 52                 tmp  =  _que . front(); _que . pop();
 53                  for (v = 0 ;v < n;v ++ )
 54                      if (  ! visi[v]  &&  tree[tmp . u][v] !=- 1  ){
 55                        visi[v] = 1 ;
 56                        best[i][v] =
57                                 (tmp . max < tree[tmp . u][v]) ? tree[tmp . u][v] : tmp . max ;
 58                        arr[total] . max = best[i][v];
 59                        arr[total] . u = v;
 60                        _que . push(arr[total]);
 61                         ++ total;
 62                     }
 63             }
 64         }
 65         unique  =   1 ;
 66          for (i = 0 ;i < n;i ++ )
 67              for (j = i + 1 ;j < n;j ++ )
 68                  if ( g[i][j] != 0x7fffffff   &&  tree[i][j] ==- 1  )
 69                      if ( t1  -  best[i][j]  +  g[i][j]  ==  t1 ) unique  =   0 ;
 70
71          if ( unique )  printf ( " %d\n " , t1);
 72          else   printf ( " Not Unique!\n " );
 73
74     }
 75
76      return   0 ;
 77 }