POJ1523 SPF（割点）

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 #define MAXM 1111*1111*2
 6 #define MAXN 1111
 7 struct Edge{
 8     int v,next;
 9 }edge[MAXM];
10 int head[MAXN],NE;
11 void addEdge(int u,int v){
12     edge[NE].v=v; edge[NE].next=head[u]; head[u]=NE++;
13 }
14 int dn,dfn[MAXN],low[MAXN],son[MAXN];
15 void dfs(int u){
16     dfn[u]=low[u]=++dn;
17     for(int i=head[u]; i!=-1; i=edge[i].next){
18         int v=edge[i].v;
19         if(dfn[v]){
20             low[u]=min(low[u],dfn[v]);
21             continue;
22         }
23         dfs(v);
24         if(u==1) ++son[u];
25         else if(low[v]>=dfn[u]) ++son[u];
26         low[u]=min(low[u],low[v]);
27     }
28 }
29 bool output(){
30     bool flag=0;
31     if(son[1]>=2) printf("  SPF node 1 leaves %d subnets\n",son[1]),flag=1;
32     for(int u=2; u<=1000; ++u){
33         if(son[u]) printf("  SPF node %d leaves %d subnets\n",u,son[u]+1),flag=1;
34     }
35     return flag;
36 }
37 int main(){
38     int u,v,t=0;
39     for(;;){
40         bool flag=1;
41         NE=0;
42         memset(head,-1,sizeof(head));
43         while(~scanf("%d",&u) && u){
44             scanf("%d",&v);
45             addEdge(u,v); addEdge(v,u);
46             flag=0;
47         }
48         if(flag) break;
49         dn=0;
50         memset(dfn,0,sizeof(dfn));
51         memset(son,0,sizeof(son));
52         dfs(1);
53         printf("Network #%d\n",++t);
54         if(!output()) puts("  No SPF nodes");
55         putchar(‘\n‘);
56     }
57     return 0;
58 }