Day65：POJ1144-Network-求割点-模板题

题目链接：POJ - 1144 

 

求割点的模板题

 

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
#include<vector>
using namespace std;

const int N=10010;
int dfn[N],low[N],f[N],n,cnt;
bool book[N];//是否是割点
vector<int>v[N];

void init()
{
    for(int i=0; i<N; i++)
        v[i].clear();
    cnt=0;
    memset(low,0,sizeof(low));
    memset(dfn,0,sizeof(dfn));
    memset(f,0,sizeof(f));
    memset(book,0,sizeof(book));
}

void Tarjan(int u,int fa)
{
    dfn[u]=low[u]=++cnt;
    f[u]=fa;
    for(int i=0; i<v[u].size(); i++)
    {
        int x=v[u][i];
        if(dfn[x]==0)
        {
            Tarjan(x,u);
            low[u]=min(low[x],low[u]);
        }
        else if(fa!=x)
            low[u]=min(dfn[x],low[u]);
    }
}

int main()
{
    while(~scanf("%d",&n)&&n)
    {
        init();
        int x,y;
        while(~scanf("%d",&x)&&x)
        {
            while(getchar()!='\n')
            {
                scanf("%d",&y);
                v[x].push_back(y);
                v[y].push_back(x);
            }
        }
        Tarjan(1,0);
        int son=0;//统计根节点儿子的个数
        for(int i=2; i<=n; i++)
        {
            x=f[i];
            if(x==1)//i的父亲是根节点
                son++;
            else if(dfn[x]<=low[i])
                book[x]=1;
        }
        int ans=0;
        if(son>1)
            ans++;
        for(int i=2; i<=n; i++)
        {
            if(book[i])
                ans++;
        }
        printf("%d\n",ans);
    }
    return 0;
}