次小生成树

  1 #include<cstdio>
  2 #include<cstring>
  3 #include<algorithm>
  4 #define _Clr(x, y) memset(x, y, sizeof(x))
  5 #define INF 0x3f3f3f3f
  6 #define N 110
  7 using namespace std;
  8 
  9 struct Edge
 10 {
 11     int a, b;
 12     int c;
 13     bool operator < (const Edge &a) const
 14     {
 15         return c < a.c;
 16     }
 17 }edge[N*N];
 18 int bleg[N], n, m;
 19 int mst_edge[N];
 20 
 21 int find(int x)
 22 {
 23     int y = x;
 24     while(y != bleg[y])
 25         y = bleg[y];
 26     while(x != bleg[x])
 27     {
 28         int px = bleg[x];
 29         bleg[x] = y;
 30         x = px;
 31     }
 32     return y;
 33 }
 34 
 35 void Union(int a, int b)
 36 {
 37     int pa=find(a), pb=find(b);
 38     if(pa != pb)
 39         bleg[pa] = pb;
 40 }
 41 
 42 inline void Init()
 43 {
 44     for(int i=0; i<=n; i++)
 45         bleg[i] = i;
 46 }
 47 
 48 void Kruskal()
 49 {
 50     int mst_1=0;
 51     Init();
 52     _Clr(mst_edge, 0);
 53     sort(edge, edge+m);
 54     int k=0;
 55     for(int i=0; i<m && k<n-1; i++)
 56     {
 57         int a=find(edge[i].a);
 58         int b=find(edge[i].b);
 59         if(a != b)
 60         {
 61             mst_edge[k] = i;
 62             Union(a, b);
 63             mst_1 += edge[i].c;
 64             k++;
 65         }
 66     }
 67     // 枚举删除最小生成树中所有边求MST
 68     for(int i=0; i<n-1; i++)
 69     {
 70         int mst_2=0, k=0;
 71         Init();
 72         for(int j=0; j<m && k<n-1; j++)
 73         {
 74             if(mst_edge[i] == j) continue;
 75             int a=find(edge[j].a);
 76             int b=find(edge[j].b);
 77             if(a != b)
 78             {
 79                 Union(a, b);
 80                 mst_2 += edge[j].c;
 81                 k++;
 82             }
 83         }
 84         if(mst_1==mst_2 && k==n-1)
 85         {
 86             puts("Not Unique!");
 87             return;
 88         }
 89     }
 90     printf("%d\n", mst_1);
 91 }
 92 
 93 int main()
 94 {
 95     int T;
 96     scanf("%d", &T);
 97     while(T--)
 98     {
 99         scanf("%d%d", &n, &m);
100         for(int i=0; i<m; i++)
101             scanf("%d%d%d", &edge[i].a, &edge[i].b, &edge[i].c);
102         Kruskal();
103     }
104     return 0;
105 }