不用Matrix-tree定理什么的，一边kruscal一边 对权值相同的边 暴搜即可。将所有方案乘起来。
1 #include<cstdio> 2 #include<algorithm> 3 using namespace std; 4 int n,m; 5 struct Disjoint_Set 6 { 7 int fa[101],rank[101]; 8 void init(){for(int i=1;i<=n;i++) fa[i]=i;} 9 int findroot(int x) 10 { 11 if(fa[x]==x) return x; 12 int rt=findroot(fa[x]); 13 fa[x]=rt; 14 return rt; 15 } 16 void Union(int U,int V) 17 { 18 if(rank[U]<rank[V]) fa[U]=V; 19 else 20 { 21 fa[V]=U; 22 if(rank[U]==rank[V]) rank[U]++; 23 } 24 } 25 }; 26 Disjoint_Set S,used; 27 struct Edge{int u,v,w;}; 28 bool cmp(const Edge &a,const Edge &b){return a.w<b.w;} 29 Edge edges[1001]; 30 int res,ans=1,tot,cnt,sta,end; 31 void dfs(int cur,int sum,Disjoint_Set now) 32 { 33 if(cur>end) 34 { 35 if(sum==cnt) res++; 36 return; 37 } 38 dfs(cur+1,sum,now); 39 int f1=now.findroot(edges[cur].u),f2=now.findroot(edges[cur].v); 40 if(f1!=f2) {now.Union(f1,f2); dfs(cur+1,sum+1,now);} 41 } 42 int main() 43 { 44 scanf("%d%d",&n,&m); 45 for(int i=1;i<=m;i++) scanf("%d%d%d",&edges[i].u,&edges[i].v,&edges[i].w); 46 sort(edges+1,edges+m+1,cmp); 47 S.init();used.init(); 48 for(int i=1;i<=m;i++) 49 { 50 if(edges[i].w!=edges[i-1].w) {used=S; cnt=0; sta=i;} 51 int f1=S.findroot(edges[i].u),f2=S.findroot(edges[i].v); 52 if(f1!=f2) {S.Union(f1,f2); tot++; cnt++;} 53 if(edges[i].w!=edges[i+1].w) 54 { 55 res=0; end=i; 56 dfs(sta,0,used); 57 ans=((ans%31011)*(res%31011))%31011; 58 } 59 else if(tot==n-1) 60 { 61 res=0; 62 for(int j=i+1;j<=m;j++) 63 if(edges[j].w!=edges[i].w) 64 { 65 end=j-1; 66 goto OUT; 67 } 68 end=m; 69 OUT:dfs(sta,0,used); 70 ans=((ans%31011)*(res%31011))%31011; 71 break; 72 } 73 } 74 printf("%d ",tot==n-1 ? ans : 0); 75 return 0; 76 }