tarjan求割点

发现之前的求割点模板有问题 ，新搞一份

#include
#include
#include
#define N 1001
using namespace std;
int n,id,tot;
int dfn[N],low[N];
bool cutpoint[N];
int front[N],to[200005],nxt[200005];
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 clear()
{
    id=0; tot=1;
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(front,0,sizeof(front));
    memset(cutpoint,0,sizeof(cutpoint));
}
int main()
{
    int x,y,ans;
    char c;
    while(scanf("%d",&n) && n)
    {
        clear();
        while(scanf("%d",&x) && x)
        {
            while((c=getchar())!='\n')
            {
                scanf("%d",&y);
                add(x,y);
            }
        }
        tarjan(1,0);
        ans=0;
        for(int i=1;i<=n;i++)
         if(cutpoint[i]) ans++;
        printf("%d\n",ans);
    }
}