poj 1523--SPF

题意：问删除某个点是否形成多个网络

思路：求割点

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int N=1002;

struct node{
    int to,next;
}e[N*N];

int head[N],tot;
int dfn[N],low[N],a[N];
int indexx;
int n;
int tt;

void init(){
    memset(head,-1,sizeof(head));
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    indexx=0;
    n=0;
    tt=0;
}

void add(int u,int v){
    e[tot].to=v;
    e[tot].next=head[u];
    head[u]=tot++;
}

void dfs(int u){
    dfn[u]=low[u]=++indexx;
    for(int i=head[u];i!=-1;i=e[i].next){
        int v=e[i].to;
        if(!dfn[v]){
            dfs(v);
            low[u]=min(low[u],low[v]);
            if(dfn[u]<=low[v]) {
                a[u]++;
            }
        }
        else low[u]=min(low[u],dfn[v]);
    }
}

int main(){
    init();
    int t=1;
    int x,y;
    while(scanf("%d",&x)){
        if(x==0) break;
        init();
        scanf("%d",&y);
        add(x,y);add(y,x);
        n=max(max(x,y),n);
        while(scanf("%d",&x)&&x){
            scanf("%d",&y);
            add(x,y);add(y,x);
            n=max(max(y,x),n);
        }
        for(int i=2;i<=n;i++) a[i]=1;
        a[1]=0;
        dfs(1);
       printf("Network #%d
",t++);
              for(int i=1;i<=n;i++)
              if(a[i]>1)
              {
                       printf("  SPF node %d leaves %d subnets
",i,a[i]);
                       tt=1;
              }
           if(!tt)printf("  No SPF nodes
");
       printf("
");
    }
    return 0;
}