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
| #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <deque>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <cmath>
#include <bitset>
#include <iterator>
#include <random>
#include <iomanip>
#include <cctype>
#include <array>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr;
const ll MAXN=160;
vector<ll> g[MAXN];
ll N,M;
pll edge[5010];
ll dfsn[MAXN],low[MAXN];
ll fa[MAXN];
ll idx=0;
bool vis[MAXN];
ll dfs(int x,int pa){
fa[x]=pa;
vis[x]=true;
dfsn[x]=++idx;
low[x]=dfsn[x];
for(int i=0;i<g[x].size();++i){
if(!vis[g[x][i]]){
low[x]=min(dfs(g[x][i],x),low[x]);
}else if(g[x][i] != pa ){
low[x]=min(dfsn[g[x][i]],low[x]);
}else if(g[x][i+1]==pa){
low[x]=min(dfsn[g[x][i]],low[x]);
}
}
return low[x];
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);cout.tie(0);
cin>>N>>M;
for(int i=1;i<=M;++i){
cin>>edge[i].first>>edge[i].second;
}
sort(&edge[1], &edge[M+1]);
for(int i=1;i<=M;++i){
g[edge[i].first].push_back(edge[i].second);
g[edge[i].second].push_back(edge[i].first);
}
dfs(1,1);
vector<pll> ans;
for(int i=1;i<=N;++i){
if(low[i]>dfsn[fa[i]]){
ll a=fa[i],b=i;
if(a>b)
swap(a, b);
ans.push_back({a,b});
}
}
sort(ans.begin(),ans.end());
for(int i=0;i<ans.size();++i){
cout<<ans[i].first<<' '<<ans[i].second<<'\n';
}
return 0;
}
|