HDU——T 3072 Intelligence System

 1 #include <algorithm>
 2 #include <cstring>
 3 #include <cstdio>
 4 
 5 using namespace std;
 6 
 7 const int INF(0x7fffffff);
 8 const int N(50000+15);
 9 const int M(100000+5);
10 int n,m,head[N],sumedge;
11 struct Edge
12 {
13     int v,next,dis;
14     Edge(int v=0,int next=0,int dis=0):
15         v(v),next(next),dis(dis){}
16 }edge[M<<1];
17 inline void ins(int u,int v,int w)
18 {
19     edge[++sumedge]=Edge(v,head[u],w);
20     head[u]=sumedge;
21 }
22 
23 int low[N],dfn[N],tim;
24 int top,Stack[N],instack[N];
25 int col[N],sumcol,val[N];
26 void DFS(int now)
27 {
28     low[now]=dfn[now]=++tim;
29     Stack[++top]=now; instack[now]=1;
30     for(int i=head[now];i;i=edge[i].next)
31     {
32         int v=edge[i].v;
33         if(!dfn[v])  DFS(v),low[now]=min(low[now],low[v]);
34         else if(instack[v]) low[now]=min(low[now],dfn[v]);
35     }
36     if(low[now]==dfn[now])
37     {
38         col[now]=++sumcol;
39         for(;Stack[top]!=now;top--)
40         {
41             col[Stack[top]]=sumcol;
42             instack[Stack[top]]=0;
43         }
44         instack[now]=0; top--;
45     }
46 }
47 
48 inline void init()
49 {
50     sumedge=sumcol=tim=top=0;
51     memset(low,0,sizeof(low));
52     memset(dfn,0,sizeof(dfn));
53     memset(col,0,sizeof(col));
54     memset(edge,0,sizeof(edge));
55     memset(head,0,sizeof(head));
56     memset(Stack,0,sizeof(Stack));
57     memset(instack,0,sizeof(instack));
58 }
59 
60 int main()
61 {
62     for(int u,v,w;~scanf("%d%d",&n,&m);init())
63     {
64         for(int i=1;i<=m;i++)
65         {
66             scanf("%d%d%d",&u,&v,&w);
67             ins(u+1,v+1,w);
68         }
69         for(int i=1;i<=n;i++)
70             if(!dfn[i]) DFS(i);
71         for(int i=1;i<=n;i++) val[i]=INF;
72         for(int u=1;u<=n;u++)
73             for(int i=head[u];i;i=edge[i].next)
74             {
75                 int v=edge[i].v;
76                 if(col[u]==col[v]) continue;
77                 val[col[v]]=min(val[col[v]],edge[i].dis);
78             }
79         long long ans=0;
80         for(int i=1;i<=sumcol;i++)
81             if(val[i]!=INF) ans+=(long long)val[i];
82         printf("%I64d\n",ans);
83     }
84     return 0;
85 }