poj 1523 SPF

#include<cstdio>
#include<cstring>
#include<algorithm>
#define N 1001
using namespace std;
int tot=1,front[N],to[N*N*2],nxt[N*N*2];
int dfn[N],low[N],id;
bool cutpoint[N],part[N];
void add(int u,int v)
{
    to[++tot]=v; nxt[tot]=front[u]; front[u]=tot;
    to[++tot]=u; nxt[tot]=front[v]; front[v]=tot;
}
void tarjan(int u,int pre)
{
    dfn[u]=low[u]=++id;
    int sum=0;
    bool tmp=false;
    for(int i=front[u];i;i=nxt[i])
    {
        if(i==(pre^1)) continue;
        if(!dfn[to[i]]) 
        {
            sum++;
            tarjan(to[i],i);
            low[u]=min(low[u],low[to[i]]);
            if(low[to[i]]>=dfn[u]) tmp=true;    
        }
        else low[u]=min(low[u],dfn[to[i]]);
    }
    if(!pre) { if(sum>1) cutpoint[u]=true; }
    else if(tmp) cutpoint[u]=true;
}
void solve()
{
    tarjan(1,0);
    bool ok=false;  int sum;
    for(int i=1;i<N;i++)
     if(cutpoint[i])
     {
         ok=true; sum=0;
         memset(part,0,sizeof(part));
         for(int j=front[i];j;j=nxt[j])
          if(!part[low[to[j]]])
          {
                part[low[to[j]]]=true;
                sum++;
          }    
        printf("  SPF node %d leaves %d subnets\n",i,sum);    
     }
    if(!ok) printf("  No SPF nodes\n");
    puts(""); 
}
void clear()
{
    tot=1; id=0;
    memset(front,0,sizeof(front));
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(cutpoint,0,sizeof(cutpoint));
}
int main()
{
    //freopen("1.txt","w",stdout);
    int u,v,t=0,last;
    while(scanf("%d",&u)!=EOF)
    {
        if(u) 
        {
            scanf("%d",&v);
            add(u,v);
        }
        else
        {
            if(!last) return 0;
            t++;
            printf("Network #%d\n",t);
            solve();
            clear();
        }
        last=u;
    }
}