Warm up

 1 #pragma comment(linker,"/STACK:100000000,100000000")//阔栈的语句
 2 #include <stdio.h>
 3 #include <string.h>
 4 #include <vector>
 5 #define pb push_back
 6 using namespace std;
 7 const int maxn = 200002;
 8 const int maxm = 1000002;
 9 struct EDGE{
10     int next, to, vis;
11 }edge[maxm*2];//记录边，vis表示这一条边是否被访问
12 struct GEEDGE {
13     int u, to;
14 }geedge[maxm];//记录割边
15 int n,m,time,top,type,getot,cnt;//time是时间戳,type标记连通块,getot割边的数量，cnt边数
16 int head[maxn],st[maxn],dfn[maxn],low[maxn],belo[maxn];//belo[i],表示i属于哪个连通块
17 int start,ans1,ans,u,v;
18 void init(){
19     time=top=type=getot=cnt=0;
20     memset(head,-1,sizeof(head));
21     memset(dfn,0,sizeof(dfn));
22     memset(low,0,sizeof(low));
23     memset(belo,0,sizeof(belo));
24 }
25 void add(int u,int v){
26    edge[cnt].to=v;
27    edge[cnt].next=head[u];
28    edge[cnt].vis=0;
29    head[u]=cnt++;
30 }
31 void dfs(int u) {
32     low[u] = dfn[u] = ++time;
33     st[++top] = u;
34     for(int i = head[u];i != -1;i = edge[i].next) {
35         if(edge[i].vis)    continue;
36         edge[i].vis = edge[i^1].vis = 1;
37         int to = edge[i].to;
38         if(!dfn[to]) {
39             dfs(to);
40             low[u] = min(low[u], low[to]);
41             if(low[to] > dfn[u]) {//表示找到一个连通块
42                 type++;
43                 int v;
44                 do {
45                     v = st[top--];
46                     belo[v] = type;//表示v属于第type个连通块
47                 } while(v != to);
48                 geedge[++getot].u = u;//记录割边的起点
49                 geedge[getot].to = to;//记录割边的另一个点
50             }
51         }
52         else
53             low[u] = min(low[u], low[to]);
54     }
55 }
56 void DFS(int len,int fa,int now){//求树的直径
57     if(len>ans){
58         ans=len;
59         start=now;
60     }
61     for(int i=head[now];i!=-1;i=edge[i].next){
62         int v=edge[i].to;
63         if(v!=fa) DFS(len+1,now,v);
64     }
65 }
66 int main(){
67      while(~scanf("%d%d",&n,&m)&&n){
68          init();
69          for(int i=1;i<=m;i++){
70             scanf("%d%d",&u,&v);
71             add(u,v);
72             add(v,u);
73          }
74          for(int i=1;i<=n;i++)
75             if(!dfn[i])
76               dfs(i);
77          ans1=getot;
78          memset(head,-1,sizeof(head));cnt=0;//刷新边，接下来从新加边
79          for(int i=1;i<=ans1;i++){
80             add(belo[geedge[i].to],belo[geedge[i].u]);
81             add(belo[geedge[i].u],belo[geedge[i].to]);
82          }
83          ans = 0;
84          DFS(0,-1,1);//
85          ans=0;
86          DFS(0,-1,start);//两遍DFS求树的直径
87         printf("%d\n", getot-ans);
88      }
89 }