求一个生成树，使得最大边权和最小边权之差最小。由于数据太小，暴力枚举下界，求出相应的上界。最后取min即可。
1 #include<cstdio> 2 #include<algorithm> 3 #include<cstring> 4 using namespace std; 5 int n,m,fa[101],rank[101]; 6 void clear(){for(int i=1;i<=n;i++) fa[i]=i; memset(rank,0,sizeof(rank));} 7 int findroot(int x) 8 { 9 if(fa[x]==x) return x; 10 int rt=findroot(fa[x]); 11 fa[x]=rt; 12 return rt; 13 } 14 void Union(int U,int V) 15 { 16 if(rank[U]<rank[V]) fa[U]=V; 17 else 18 { 19 fa[V]=U; 20 if(rank[U]==rank[V]) rank[U]++; 21 } 22 } 23 struct Edge{int u,v,w;}; 24 bool cmp(const Edge &a,const Edge &b){return a.w<b.w;} 25 Edge edges[5001]; 26 int tot,ans,maxv; 27 int main() 28 { 29 while(1) 30 { 31 scanf("%d%d",&n,&m); 32 if(!n) break; 33 for(int i=1;i<=m;i++) scanf("%d%d%d",&edges[i].u,&edges[i].v,&edges[i].w); 34 sort(edges+1,edges+m+1,cmp); ans=2147483647; 35 for(int j=1;j<=m;j++) 36 { 37 tot=0; clear(); 38 for(int i=j;i<=m;i++) 39 { 40 int f1=findroot(edges[i].u),f2=findroot(edges[i].v); 41 if(f1!=f2) {Union(f1,f2); tot++; if(tot==n-1) {maxv=edges[i].w; goto WIN;}} 42 } 43 continue; 44 WIN:ans=min(ans,maxv-edges[j].w); 45 } 46 printf("%d ",ans!=2147483647 ? ans : -1); 47 } 48 return 0; 49 }