hdu4612 卡cin e-DCC缩点

/*
给定无向图，求加入一条边后最少剩下多少桥
*/
#include<bits/stdc++.h>
using namespace std;
#define maxn 200005
#define maxm 1000005
struct Edge{int to,nxt,cut;}edge[maxm<<1],edge_c[maxm<<1];
int head[maxn],tot,head_c[maxn],tot_c,n,m,q;

void addedge(int u,int v){
    edge[tot].to=v;edge[tot].nxt=head[u];head[u]=tot++;
    edge[tot].cut=0;
}
void add_c(int u,int v){
    edge_c[tot_c].to=v;
    edge_c[tot_c].nxt=head_c[u];
    head_c[u]=tot_c++;
}

int dfn[maxn],low[maxn],ind,c[maxn],dcc;
void tarjan(int u,int in_edge){
    dfn[u]=low[u]=++ind;
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(!dfn[v]){
            tarjan(v,i);
            low[u]=min(low[u],low[v]);
            
            if(dfn[u]<low[v])
                edge[i].cut=edge[i^1].cut=1;
        }
        else if(i!=(in_edge^1)) 
            low[u]=min(low[u],dfn[v]); 
    }
}
void dfs1(int u){
    c[u]=dcc;
    for(int i=head[u];i!=-1;i=edge[i].nxt){
        int v=edge[i].to;
        if(c[v]||edge[i].cut)continue;
        dfs1(v);
    }
}

int dep[maxn],fa[maxn],flag[maxn];//flag[u]表示u上点的边使割边 
void dfs2(int u,int pre,int deep){
    dep[u]=deep;fa[u]=pre;flag[u]=1;
    for(int i=head_c[u];i!=-1;i=edge_c[i].nxt){
        int v=edge_c[i].to;
        if(v==pre)continue;
        dfs2(v,u,deep+1);
    }
}

void init(){
    memset(head,-1,sizeof head);
    memset(head_c,-1,sizeof head_c);
    memset(dep,0,sizeof dep);
    memset(fa,0,sizeof fa);
    memset(flag,0,sizeof flag);
    memset(c,0,sizeof c);
    memset(dfn,0,sizeof dfn);
    memset(low,0,sizeof low);
    tot=tot_c=ind=dcc=0;
}
int main(){
    int tt=0;
    while(cin>>n>>m,n){
        init();
        for(int i=1;i<=m;i++){
            int u,v;
            scanf("%d%d",&u,&v);
            addedge(u,v);
            addedge(v,u);
        }
        tarjan(1,0);
        
        dcc=0;//染色 
        for(int i=1;i<=n;i++)
            if(!c[i]){
                ++dcc;
                dfs1(i); 
            }
        
        
        for(int i=0;i<tot;i++){//缩点 
            int v=edge[i].to,u=edge[i^1].to;
            if(c[u]==c[v])continue;
            add_c(c[u],c[v]);  
        }
        
        int Max=-1,root=1;
        dfs2(root,0,0);
        for(int i=1;i<=dcc;i++)
            if(Max<dep[i]){
                Max=dep[i];
                root=i;
            }
        memset(dep,0,sizeof dep);
        dfs2(root,0,0);
        for(int i=1;i<=dcc;i++)
            Max=max(Max,dep[i]);
        
        cout<<dcc-1-Max<<endl;
  
    }
    return 0;
}