【POJ】1679 The Unique MST

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 #include <cstring>
 5 using namespace std;
 6 const int maxn = 110;
 7 const int inf = 0x3f3f3f3f;
 8 
 9 bool vis[maxn];
10 int lowc[maxn];
11 int pre[maxn];
12 int Max[maxn][maxn];//Max[i][j]表示在最小生成树中从i到j的路径中的最大边权
13 bool used[maxn][maxn];
14 int mp[maxn][maxn];
15 int n,m;
16 
17 
18 int prim(){
19     int ans = 0;
20     memset(vis,false,sizeof(vis));
21     memset(Max,0,sizeof(Max));
22     memset(used,false,sizeof(used));
23     
24     vis[0] = true;
25     pre[0] = -1;
26     
27     for(int i = 1; i < n; i++){
28         lowc[i] = mp[0][i];
29         pre[i] = 0;
30     }
31 
32     lowc[0] = 0;
33     for(int i = 1 ; i < n;i++){
34         int minc = inf;
35         int p = -1;
36         for(int j = 0; j < n;j++)
37             if(!vis[j] && minc > lowc[j]){
38                 minc = lowc[j];
39                 p = j;
40             }
41         if(minc == inf) return -1;
42         ans += minc;
43         vis[p] = true;
44         used[p][ pre[p] ] = used[ pre[p] ][p] = true;
45         for(int j = 0 ; j < n; j++){
46             if(vis[j])
47                 Max[j][p] = Max[p][j] = max(Max[j][ pre[p] ],lowc[p]);
48             if(!vis[j] && (lowc[j] > mp[p][j] ) ){
49                 lowc[j] = mp[p][j];
50                 pre[j] = p;
51             }
52         }
53     }
54     return ans;
55 }
56 int ans;
57 int smst(){
58     int minn = inf;
59     for(int i = 0; i < n; i++)
60         for(int j = i+1 ; j < n;j++)
61             if(mp[i][j] != inf && !used[i][j]){
62                 minn = min(minn, ans + mp[i][j] - Max[i][j]);
63             }
64     if(minn == inf) return -1;//不存在
65     return minn;
66 }
67 
68 int main(){
69     int T;
70     cin>>T;
71     while(T--){
72         cin>>n>>m;
73         int x,y,w;
74         memset(mp,inf,sizeof(mp)); 
75         for(int i = 0; i < n ;i++){
76             mp[i][i] = 0;
77         }
78         while(m--){
79             cin>>x>>y>>w;
80             x--,y--;
81             mp[x][y] = mp[y][x] = w;
82         }
83         ans = prim();
84         //cout<<smst()<<endl;
85         if(ans == -1){
86             cout<<"Not Unique!"<<endl;
87         }
88         else if( ans == smst()){
89             cout<<"Not Unique!"<<endl;   
90         }
91         else{
92             cout<<ans<<endl;
93         }
94     }
95     
96     return 0;
97 }