1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
|
#include<iostream>
#include<cstdio>
#include<vector>
#include<cstring>
using namespace std;
long long read()
{
long long x=0,f=1; char c=getchar();
while(!isdigit(c)){if(c=='-') f=-1;c=getchar();}
while(isdigit(c)){x=x*10+c-'0';c=getchar();}
return x*f;
}
const int N=1000+10;
vector <int> e[N],e2[N];
int dfn[N],dfn_to,low[N],mstack[N],top,belong[N],cnt;
bool vis[N],InStack[N];
void Tarjan(int now,int father)
{
vis[now]=InStack[now]=true;
mstack[++top]=now;
dfn[now]=low[now]=++dfn_to;
for(int i=0;i<int(e[now].size());i++)
if(vis[e[now][i]]==false)
{
Tarjan(e[now][i],now);
low[now]=min(low[now],low[e[now][i]]);
}
else if(e[now][i]!=father and InStack[e[now][i]]==true)
low[now]=min(low[now],dfn[e[now][i]]);
if(low[now]==dfn[now])
{
cnt++;
while(mstack[top+1]!=now)
InStack[mstack[top]]=false,
belong[mstack[top--]]=cnt;
}
}
int Find(int now,int x)
{
for(int i=0;i<int(e[now].size());i++)
if(e[now][i]==x)
return i;
return -1;
}
void dfs2(int now)
{
if(vis[now]==true) return;
vis[now]=true;
for(int i=0;i<int(e[now].size());i++)
if(belong[e[now][i]]==belong[now])
{
printf("%d %d\n",now,e[now][i]);
e[e[now][i]][Find(e[now][i],now)]=0;
dfs2(e[now][i]);
}
}
int n,m;
int main()
{
for(int o=1;;o++)
{
n=read(),m=read();
if(n==0 and m==0) break;
for(int i=0;i<=n;i++)
e[i].clear(),e2[i].clear();
for(int i=1;i<=n;i++)
e[i].reserve(4),e2[i].reserve(4);
for(int i=1;i<=m;i++)
{
int s=read(),t=read();
e[s].push_back(t);
e[t].push_back(s);
}
memset(vis,0,sizeof vis);
memset(mstack,0,sizeof mstack);
dfn_to=cnt=0;
Tarjan(1,0);
printf("%d\n\n",o);
memset(vis,0,sizeof vis);
for(int i=1;i<=n;i++)
dfs2(i);
for(int i=1;i<=n;i++)
for(int j=0;j<int(e[i].size());j++)
if(belong[i]!=belong[e[i][j]] and e[i][j]!=0)
printf("%d %d\n",i,e[i][j]);
printf("#\n");
}
return 0;
}
|
