COGS——T 8. 备用交换机

 1 #include<algorithm>
 2 #include<cstring>
 3 #include<cstdio>
 4 #define N 1100
 5 using namespace std;
 6 int n,x,y,tim,tot=1,ans;
 7 int dfn[N],low[N],head[N],cut_point[N];
 8 int read()
 9 {
10     int x=0,f=1; char ch=getchar();
11     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1; ch=getchar();}
12     while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘; ch=getchar();}
13     return x*f;
14 }
15 struct Edge
16 {
17     int to,from,next;
18 }edge[N];
19 int add(int x,int y)
20 {
21     tot++;
22     edge[tot].to=y;
23     edge[tot].next=head[x];
24     head[x]=tot;
25 }
26 int tarjan(int now,int pre)
27 {
28     int sum=0;bool if_point=false;
29     dfn[now]=low[now]=++tim;
30     for(int i=head[now];i;i=edge[i].next)
31     {
32         int t=edge[i].to;
33         if((i^1)==pre) continue;
34         if(!dfn[t])
35         {
36             sum++,tarjan(t,i);
37             low[now]=min(low[now],low[t]);
38             if(dfn[now]<=low[t]) if_point=true;
39         }
40         else low[now]=min(low[now],dfn[t]);
41     }
42     if(!pre){if(sum>1) ans++,cut_point[now]=true;}
43     else if(if_point) ans++,cut_point[now]=true;
44 }
45 int main()
46 {
47     freopen("gd.in","r",stdin);
48     freopen("gd.out","w",stdout);
49     
50     n=read();
51     while(scanf("%d%d",&x,&y)==2)
52      add(x,y),add(y,x);
53     for(int i=1;i<=n;i++) 
54      if(!dfn[i]) tarjan(i,0);
55     printf("%d\n",ans);
56     for(int i=1;i<=n;i++)
57      if(cut_point[i]) printf("%d\n",i);
58 }