POJ1144 Network（判断割点）

题目链接“点击打开链接

判断割点的个数

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
const int N = 210;
const int maxn = 500;
const int maxm = 21010;
const int inf = 1e8;
#define MIN INT_MIN
#define MAX 1e6
#define LL long long
#define init(a) memset(a,0,sizeof(a))
#define FOR(i,a,b) for(int i = a;i<b;i++)
#define max(a,b) (a>b)?(a):(b)
#define min(a,b) (a>b)?(b):(a)
using namespace std;

int DFN[maxn],low[maxn],head[maxn];
bool dian[maxn];
int bianhao,n,bnum,root,vis[maxn];
int gedian[maxn],ge;
struct edge
{
    int v,next;
}edge[maxm];

void add(int u,int v)
{
    edge[bnum].v=v;
    edge[bnum].next=head[u];
    head[u]=bnum++;
}

void tarjan(int u,int father)//判定割点
{
    int son=0;
    vis[u]=1;//标记
    DFN[u]=low[u]=bianhao++;
    for(int i=head[u];i!=-1;i=edge[i].next)
    {
        int v=edge[i].v;
        if(vis[v]==1 && v!=father)
            low[u]=min(low[u],DFN[v]);
        if(vis[v]==0)
        {
            tarjan(v,u);
            son++;
            low[u]=min(low[u],low[v]);
            if((u==root && son>1 ) || (u!=root && DFN[u]<=low[v]))//判定割点的条件
            {
               dian[u]=1;
            }
        }
    }
    vis[u]=2;//去掉
}
void initt()
{
        memset(head,-1,sizeof(head));
        init(DFN);init(low);
        init(vis);init(dian);
        bnum=0;bianhao = 1;//ge = 0;
}
int main()
{
    int a,b;
    while(scanf("%d",&n),n)
    {
        initt();
        while(scanf("%d",&a),a)
        {
            while(getchar()!='\n')
            {
                scanf("%d",&b);
                add(a,b);
                add(b,a);
            }
        }
        root=1;
        tarjan(1,-1);
        int ans = 0;
        FOR(i,1,n+1)
        {
            if(dian[i]!=0)
            {
                ans++;
               // gedian[ge++] = i;
            }
        }
        cout<<ans<<endl;
       // puts("割点是");
      /* printf("ge = %d\n",ge);
        FOR(i,0,ge)
        printf("%d ",gedian[i]);
        printf("\n");*/
    }
    return 0;
}