POJ 2117 Electricity 割点

http://poj.org/problem?id=2117

题意：给出一个无向图，不一定连通。问去掉一个点后，图最多分成几部分（几个连通图)

第一个割点题

代码：

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#define Max(a,b)a>b?a:b
#define Min(a,b)a<b?a:b
#define nMAX 10005
#define mMAX 2000010
using namespace std;
int head[nMAX],low[nMAX],dfn[nMAX],cut[nMAX];
int s_edge,times,root;
bool vs[nMAX];
struct Edge
{
    int u,v,nxt;
}edge[mMAX];
void addedge(int u,int v)
{
    edge[++s_edge].v=v;
    edge[s_edge].nxt=head[u];
    head[u]=s_edge;

    edge[++s_edge].v=u;
    edge[s_edge].nxt=head[v];
    head[v]=s_edge;
}
void  dfs(int u,int fa)
{
    int son=0;
    dfn[u]=low[u]=++times;
    vs[u]=1;
    for(int e=head[u];e;e=edge[e].nxt)
    {
        int v=edge[e].v;
        if(!vs[v])
        {
            son++;
            dfs(v,u);
            low[u]=Min(low[u],low[v]);
            if((u==root&&son>1)||(u!=root&&low[v]>=dfn[u]))//low[v]>dfn[u]!!!
             cut[u]++;
        }
        else if(v!=fa)
        low[u]=Min(low[u],dfn[v]);
    }
}
void init()
{
    memset(head,0,sizeof(head));
    memset(cut,0,sizeof(cut));
    memset(vs,0,sizeof(vs));
    memset(dfn,0,sizeof(dfn));
    s_edge=0;
    times=0;
}
int main()
{
    int n,m,i,j;
    while(~scanf("%d%d",&n,&m))
    {
        if(n==0&&m==0)
         break;
        if(m==0)
        {printf("%d\n",n-1);continue;}
        init();
        while(m--)
        {
            scanf("%d%d",&i,&j);
            addedge(i,j);
        }
        int ans=0,MAX=0;
        for(i=0;i<n;i++)
        {
            if(!vs[i])
            {
                root=i;
                dfs(i,-1);
                ans++;
            }
            MAX=Max(MAX,cut[i]);
        }
        printf("%d\n",MAX+ans);
    }
    return 0;
}