hdu3072 Intelligence System (最小树形图？）

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<vector>
 5 #include<queue>
 6 #include<cmath>
 7 #include<ctime>
 8 #define LL long long int
 9 using namespace std;
10 const int maxn=50050,maxm=100010;
11 
12 LL rd(){
13     LL x=0;char c=getchar();int neg=1;
14     while(c<‘0‘||c>‘9‘){if(c==‘-‘) neg=-1;c=getchar();}
15     while(c>=‘0‘&&c<=‘9‘) x=x*10+c-‘0‘,c=getchar();
16     return x*neg;
17 }
18 
19 struct Edge{
20     int a,b,l,ne;
21 }eg[maxm];
22 int egh[maxn],ect;
23 int N,M;
24 int dfn[maxn],low[maxn],bel[maxn],stk[maxn],tot,pct,sct;
25 bool instk[maxn];
26 int mi[maxn];
27 
28 inline void adeg(int a,int b,int l){
29     eg[ect].a=a;eg[ect].b=b;eg[ect].l=l;eg[ect].ne=egh[a];egh[a]=ect++;
30 }
31 
32 void tarjan(int x){
33     dfn[x]=low[x]=++tot;
34     stk[++sct]=x;instk[x]=1;
35     for(int i=egh[x];i!=-1;i=eg[i].ne){
36         int j=eg[i].b;
37         if(instk[j]) low[x]=min(low[x],dfn[j]);
38         else if(!dfn[j]){
39             tarjan(j);low[x]=min(low[x],low[j]);
40         }
41     }
42     if(low[x]==dfn[x]){
43         ++pct;
44         while(sct){
45             instk[stk[sct]]=0;
46             bel[stk[sct]]=pct;
47             if(stk[sct--]==x) break;
48         }
49     }
50 }
51 
52 int main(){
53     int i,j,k;
54     while(~scanf("%d%d",&N,&M)){
55         memset(egh,-1,sizeof(egh));
56         memset(dfn,0,sizeof(dfn));
57         memset(instk,0,sizeof(instk));
58         ect=tot=pct=sct=0;
59         for(i=1;i<=M;i++){
60             int a=rd(),b=rd(),c=rd();
61             adeg(a,b,c);
62         }
63         
64         for(i=0;i<N;i++) if(!dfn[i]) tarjan(i);
65         memset(mi,127,sizeof(mi));
66         for(i=0;i<ect;i++){
67             if(bel[eg[i].a]==bel[eg[i].b]) continue;
68             mi[bel[eg[i].b]]=min(mi[bel[eg[i].b]],eg[i].l);
69         }int ans=0;
70         for(i=1;i<=pct;i++){
71             if(i!=bel[0]) ans+=mi[i];
72         }printf("%d\n",ans);
73     }
74 }