UVA-1395 Slim Span

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 #include<vector>
 5 using namespace std;
 6 #define inf 0x7f7f7f7f
 7 #define rep(i,n) for(int (i)=0;(i)<(n);i++)
 8 #define ABS(x,y) (x-y>0)?(x-y):(y-x)
 9 #define mem(a) memset(a,0,sizeof(a));
10 #define in(a) cin>>a
11 #define out(a) cout<<a
12 const int maxn=110;
13 struct Edge
14 {
15     int u;
16     int v;
17     int w;
18     Edge(int u,int v,int w):u(u),v(v),w(w){}
19 };
20 int n,m; int p[maxn];
21 int cmp(const Edge& a,const Edge& b){
22     return a.w<b.w;
23 }
24 int find(int x){
25     return p[x]==x?x:p[x]=find(p[x]);
26 }
27 int main()
28 {   //freopen("input.txt","r",stdin);
29     while(scanf("%d%d", &n, &m) == 2 && (n || m)){
30         vector<Edge> e; int u,v,w;
31         for(int i=0;i<m;i++){
32             scanf("%d%d%d", &u, &v, &w);
33             e.push_back(Edge(u,v,w));
34         }
35         sort(e.begin(),e.end(),cmp);
36         int ans=inf; int sign=0;
37         for(int L=0;L<e.size();L++){
38             for(int i=0;i<=n;i++) p[i]=i;
39             int cnt=0; int beg=e[L].w;
40             int end=beg;
41             for(int R=L;R<e.size();R++){
42                 int x=find(e[R].u);;int y=find(e[R].v);
43                 if(x!=y){
44                     ++cnt;
45                     p[x]=y;
46                     end=max(end,e[R].w);
47                 }
48                 if(cnt==n-1) break;
49             }
50             if(cnt==n-1){
51                 sign=1;
52                 ans=min(ans,end-beg);
53             }
54         }
55         if(sign==1) printf("%d\n", ans);
56         else printf("-1\n");
57     }
58     return 0;
59 }