[poj1144]Network（求割点模板）

解题关键：割点模板题。

#include<cstdio>
#include<cstring>
#include<vector>
#include<stack>
using namespace std;
#define N 1010
int n,m,ans,pd,son,cut[N],low[N],dfn[N];
stack<int>s;
const int maxn=1e5+3;
struct Edge{
    int nxt;
    int to;
    int w;
}e[maxn];
int head[maxn],cnt;
void add_edge(int u,int v){
    e[cnt].to=v;
    e[cnt].nxt=head[u];
    head[u]=cnt++;
}
void tarjan(int u){
    low[u]=dfn[u]=++pd;
    for(int i=head[u];i!=-1;i=e[i].nxt){
        int v=e[i].to;
        if(!dfn[v]){
            tarjan(v);
            low[u]=min(low[u],low[v]);
            if(low[v]>=dfn[u]&&u!=1) cut[u]++;
            else if(u==1) son++;
        }
        else low[u]=min(low[u],dfn[v]);
    }
}
int main(){
    while(scanf("%d",&n)==1&&n){
        int u,v;
        memset(dfn,0,sizeof dfn);
        memset(cut,0,sizeof cut);
        memset(head,-1,sizeof head);
        pd=ans=son=0;
        while(scanf("%d",&u)==1&&u){
            while(getchar()!='
'){
                scanf("%d",&v);
                add_edge(u,v);
                add_edge(v,u);
            }
        }
        tarjan(1);
        for(int i=1;i<=n;i++) if(cut[i]) ans++;
        if(son>1) ans++;
        printf("%d
",ans);
    }
    return 0;
}