POJ1523SPF[无向图割点]

//
//  main.cpp
//  poj1523
//
//  Created by Candy on 9/26/16.
//  Copyright © 2016 Candy. All rights reserved.
//

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
const int N=1e3+5,INF=1e9+5;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();}
    return x;
}
int n=0,u,v,w,cas=0;
struct edge{
    int v,ne;
}e[N*N];
int h[N],cnt=0;
inline void ins(int u,int v){
    cnt++;
    e[cnt].v=v;e[cnt].ne=h[u];h[u]=cnt;
    cnt++;
    e[cnt].v=u;e[cnt].ne=h[v];h[v]=cnt;
}
int pre[N],sn[N],dc=0;
int dfs(int u,int fa){
    int lowu=pre[u]=++dc,child=0;
    for(int i=h[u];i;i=e[i].ne){
        int v=e[i].v;
        if(!pre[v]){
            child++;
            int lowv=dfs(v,u);
            lowu=min(lowu,lowv);
            if(lowv>=pre[u]) sn[u]++;//,printf("v %d %d\n",u,v);
        }else if(pre[v]<pre[u]&&v!=fa)
            lowu=min(lowu,pre[v]);
    }
    if(fa==-1&&child==1) sn[u]=0;
    return lowu;
}
int main(int argc, const char * argv[]) {
    while((u=read())){
        int root=0,flag=0; n=0;
        memset(h,0,sizeof(h)); cnt=0;
        memset(pre,0,sizeof(pre));
        memset(sn,0,sizeof(sn));
        v=read();
        ins(u,v);
        n=max(n,max(u,v));
        while((u=read())){
            v=read();
            ins(u,v);
            n=max(n,max(u,v)); root=u;
        }
        dfs(root,-1);
        if(sn[root]!=0) sn[root]--;
        printf("Network #%d\n",++cas);
        for(int i=0;i<=n;i++) if(sn[i]){
            printf("  SPF node %d leaves %d subnets\n",i,sn[i]+1);
            flag=1;
        }
        if(!flag) printf("  No SPF nodes\n");
        printf("\n");
    }
    
    return 0;
}