POJ 2377

 1 #include<iostream>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<vector>
 5 #include<queue>
 6 #include<functional>
 7 using namespace std;
 8 #define MAX_V 6565
 9 
10 struct  edge
11 {
12     int to,cost;
13     edge(int to,int cost)
14     {
15         this->to=to;
16         this->cost=cost;
17     }
18 };
19 typedef pair<int ,int >P;
20 vector<edge>G[MAX_V];
21 int maxcost[MAX_V];
22 bool used[MAX_V];
23 int  V,M;
24 
25 int prim()
26 {
27     int res=0;
28     //求解最大生成树要注意元素是从大到小取出的
29     priority_queue<P>que;
30     memset(used,0,V*sizeof(bool));
31     memset(maxcost,0,sizeof(int)*MAX_V);
32     maxcost[0]=0;
33     que.push(P(0,0));
34     while(!que.empty())
35     {
36         P p=que.top();
37         que.pop();
38         int v=p.second;
39         if(maxcost[v]>p.first || used[v])
40         {
41             continue;
42         }
43         used[v]=true;
44         res+=maxcost[v];
45         for(int i=0;i<G[v].size();i++)
46         {
47             edge e=G[v][i];
48             if(maxcost[e.to]<e.cost)
49             {
50                 maxcost[e.to]=e.cost;
51                 que.push(P(maxcost[e.to],e.to));
52             }
53         }
54     }
55     return res;
56 }
57 
58 bool connect()
59 {
60     for(int i=0;i<V;i++)
61     {
62         if(used[i]==0)
63         {
64             return false;
65         }
66     }
67     return true;
68 }
69 
70 int main()
71 {
72     cin>>V>>M;
73     while(M--)
74     {
75         int A,B,T;
76         cin>>A>>B>>T;
77         A--;
78         B--;
79         G[A].push_back(edge(B,T));
80         G[B].push_back(edge(A,T));
81     }
82     int ans=prim();
83     if(connect())
84     {
85         cout<<ans<<endl;
86     }
87     else
88     {
89         cout<<-1<<endl;
90     }
91     return 0;
92 }