POJ 1523 Tarjan求割点

思路：
Tarjan

        if(dfn[x]<=low[v[i]]){
            if(x!=1)sub[x]++;
            else S++;
        }

//By SiriusRen
#include <cstdio>
#include <cstring>
#include <algorithm>
#define N 1005
using namespace std;
int xx,yy,first[N],next[N*N*2],v[N*N*2],tot,cnt,T,S,sub[N],f,cases;
int dfn[N],low[N],vis[N];
void add(int x,int y){v[tot]=y,next[tot]=first[x],first[x]=tot++;}
void tarjan(int x,int fa){
    dfn[x]=low[x]=++cnt;
    for(int i=first[x];~i;i=next[i]){
        if(!dfn[v[i]]){
            tarjan(v[i],x);low[x]=min(low[x],low[v[i]]);
            if(dfn[x]<=low[v[i]]){
                if(x!=1)sub[x]++;
                else S++;
            }
        }
        else low[x]=min(low[x],dfn[v[i]]);
    }
}
int main(){
    memset(first,-1,sizeof(first));
    while(scanf("%d",&xx)&&xx){
        st:scanf("%d",&yy);
        add(xx,yy),add(yy,xx);
    }
    tarjan(1,-1);
    T=1;
    printf("Network #%d
",++cases);
    if(S>1)sub[1]=S-1;
    for(int i=1;i<=1000;i++)
        if(sub[i])printf("  SPF node %d leaves %d subnets
",i,sub[i]+1),f=1;
    if(!f)puts("  No SPF nodes");
    puts("");
    scanf("%d",&xx);
    if(xx==0)return 0;
    else{
        tot=cnt=S=f=0;
        memset(sub,0,sizeof(sub));
        memset(first,-1,sizeof(first));
        memset(dfn,0,sizeof(dfn));
        memset(vis,0,sizeof(vis));
        goto st;
    }
}