POJ——T1679 The Unique MST

 1 #include <algorithm>
 2 #include <cstdio>
 3 
 4 using namespace std;
 5 
 6 const int N(10001);
 7 int num,n,m;
 8 int fa[N],cnt;
 9 int Fir,MST;
10 int u,v,w,used[N];
11 struct Edge
12 {
13     int u,v,w;
14 } edge[N<<1];
15 
16 bool cmp(Edge a,Edge b)
17 {
18     return a.w<b.w;
19 }
20 
21 int find(int x)
22 {
23     return fa[x]==x?x:fa[x]=find(fa[x]);
24 }
25 
26 int Kruskal()
27 {
28     int ans=0; cnt=0;
29     sort(edge+1,edge+m+1,cmp);
30     for(int i=1; i<=n; i++) fa[i]=i;
31     for(int i=1; i<=m; i++)
32     {
33         int fx=find(edge[i].u),fy=find(edge[i].v);
34         if(fx!=fy)
35         {
36             fa[fx]=fy;
37             used[++cnt]=i;
38             ans+=edge[i].w;
39         }
40         if(cnt==n-1) return ans;
41     }
42     return ans;
43 }
44 
45 int SecKru(int cant)
46 {
47     int ans=0; cnt=0;
48     for(int i=1;i<=n;i++) fa[i]=i;
49     for(int i=1;i<=m;i++) 
50     {
51         if(cant==i) continue;
52         int fx=find(edge[i].u),fy=find(edge[i].v);
53         if(fx!=fy)
54         {
55             cnt++;
56             fa[fx]=fy;
57             ans+=edge[i].w;
58         }
59         if(cnt==n-1) return ans;
60     }
61     return 0x7fffffff;
62 }
63 
64 int main() 
65 {
66     scanf("%d",&num);
67     for(;num--;)
68     {
69         scanf("%d%d",&n,&m);
70         for(int i=1;i<=m;i++) 
71             scanf("%d%d%d",&edge[i].u,&edge[i].v,&edge[i].w);
72         Fir=Kruskal(); MST=0x7fffffff;
73         for(int i=1;i<n;i++)
74         {
75             MST=min(SecKru(used[i]),MST);
76         }
77         if(Fir==MST)
78               printf("Not Unique!\n");
79         else  printf("%d\n",Fir);
80     }
81     return 0;
82 }