poj1144 求割点的个数

题目链接：http://poj.org/problem?id=1144
学习资料：https://www.byvoid.com/blog/biconnect
求割点，模板题

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <stack>
using namespace std;
const int M = 1009;
int n,m;
int dfn[M],low[M];
int dfs_clock;
bool iscut[M];
vector<int> G[M];
void init()
{
    dfs_clock = 0;
    for(int i = 0;i <= 2*n;i++) G[i].clear();
    memset(dfn,0,sizeof(dfn));
    memset(iscut,false,sizeof(iscut));
}
int dfs(int u,int fa)
{
    int lowu = dfn[u] = ++dfs_clock;
    int child = 0;
    for(int i = 0;i < G[u].size();i++)
    {
        int v = G[u][i];
        if(!dfn[v])
        {
            child++;
            int lowv = dfs(v,u);
            lowu = min(lowu,lowv);
            if(lowv >= dfn[u]) iscut[u] = true;
        }
        else if(dfn[v] < dfn[u] && v != fa)
        {
            lowu = min(lowu,dfn[v]);
        }
    }
    if(fa < 0 && child == 1) iscut[u] = false;
    low[u] = lowu;
    return lowu;
}
int main()
{
    while(scanf("%d",&n) == 1 && n)
    {
        int a;
        init();
        while(scanf("%d",&a) == 1 && a)
        {
            while(getchar() != '\n')
            {
                int b;
                scanf("%d",&b);
                G[a].push_back(b);
                G[b].push_back(a);
            }
        }
        dfs(1,-1);
        int ans = 0;
        for(int i = 1;i <= n;i++)
        {
            if(iscut[i]) ans++;
        }
        printf("%d\n",ans);
    }
    return 0;
}