POJ 1523 (割点+连通分量)

#include "cstdio"
#include "vector"
#include "string"
#include "iostream"
#include "cstring"
using namespace std;
#define maxn 1005
struct Edge
{
int next,to;
}e[maxn*2];
int pre[maxn],dfs_clock,block,head[maxn],tol;
bool cut[maxn],vis[maxn];
void addedge(int u,int v)
{
e[tol].to=v;
e[tol].next=head[u];
head[u]=tol++;
}
int dfs(int u,int fa)
{
int lowu=pre[u]=++dfs_clock;
int child=0;
for(int i=head[u];i!=-1;i=e[i].next)
{
int v=e[i].to;
if(!pre[v])
{
child++;
int lowv=dfs(v,u);
lowu=min(lowu,lowv);
if(lowv>=pre[u]) cut[u]=true;
}
else if(pre[v]<pre[u]&&v!=fa) lowu=min(lowu,pre[v]);
}
if(fa<0&&child==1) cut[u]=false;
return lowu;
}
void check(int u,int fa)
{
vis[u]=true;
for(int i=head[u];i!=-1;i=e[i].next)
{
int v=e[i].to;
if(!vis[v])
{
if(u==fa) block++;
check(v,fa);
}
}
}
int main()
{
//freopen("in.txt","r",stdin);
int u,v,num=0,no=0;
bool flag=false;
memset(head,-1,sizeof(head));
while(scanf("%d",&u)!=EOF)
{
if(!u)
{
if(!tol) break;
printf("Network #%d\n",++no);
for(int i=1;i<=num;i++) if(!pre[i]) dfs(i,-1);
bool flag=false;
for(int i=1; i<=num; i++)
if(cut[i])
{
flag=true;
check(i,i);
printf("  SPF node %d leaves %d subnets\n",i,block);
memset(vis,0,sizeof(vis));
block=0;
}
if(!flag) cout<<"  No SPF nodes"<<endl;
memset(pre,0,sizeof(pre));
memset(cut,false,sizeof(cut));
memset(head,-1,sizeof(head));
dfs_clock=0;num=0;tol=0;
printf("\n");
}
else
{
scanf("%d",&v);num=max(num,max(u,v));
addedge(u,v);
addedge(v,u);
}
}
}