POJ 1144 割点

 

题意 ：求割点的数量

#include<iostream>
#include<stdio.h>
#include<vector>
#include<string.h>
#include<stdlib.h>
using namespace std;
const int maxn = 1e5+10;
int dfn[maxn], low[maxn];
int cut[maxn];
int n,m,num,sol;
vector<int> g[maxn];
void init()
{
    memset(dfn,0,sizeof(dfn));
    memset(cut,0,sizeof(cut));
    for(int i=0;i<=n;i++) g[i].clear();
    num=sol=0;
}
void tarjan(int u,int fa)
{
    int children = 0;
    dfn[u] = low[u] = ++num;
    for (int i=0;i<g[u].size();i++)
    {
        int v=g[u][i];
        if (!dfn[v])
        {
            children++;
            tarjan(v,u);
            low[u] = min(low[u], low[v]);
            if ((fa == -1 && children >= 2)||(fa != -1 && low[v] >= dfn[u]))
                cut[u]=1;
        }
        else if (v != fa)
            low[u] = min(low[u], dfn[v]);
    }
}
int main()
{
    while(scanf("%d",&n)!=EOF&&n)
    {
        int x,y;
        init();
        while(scanf("%d",&x)&&x)
        {
            while(getchar()!='\n')
            {
                scanf("%d",&y);
                g[x].push_back(y);
                g[y].push_back(x);
            }
        }
        tarjan(1,-1);
        for(int i=0;i<=n;i++)
            if(cut[i])sol++;
        printf("%d\n",sol);
    }
}