Language: C++

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5+3;
vector<int> v[N];
bool vis[N];
list<int> L;
int n,m;
void dfs(int u, bool ok){
	for(int i=0; i<v[u].size(); ++i){ 
		if(!vis[v[u][i]]){
			if(ok) L.push_front(v[u][i]);
			else L.push_back(v[u][i]);
			vis[v[u][i]] = true;
			dfs(e,ok);
			return;
		}
	}
}
int main(){
	scanf("%d%d",&n,&m);
	memset(vis,false,sizeof(vis));
	while(m--){
		int a,b;
		scanf("%d%d",&a,&b);
		v[a].push_back(b);
		v[b].push_back(a);
	}
	L.push_back(1);
	L.push_back(v[1][0]);
	vis[1]=vis[v[1][0]]=true;
	dfs(1,true);
	dfs(v[1][0], false);
	printf("%d\n",L.size());
	for(auto it=L.begin(); it!=L.end(); ++it)
		printf("%d ",*it);
	printf("\n");
	return 0;
}#include<bits/stdc++.h>
using namespace std;
const int N = 1e5+3;
vector<int> v[N];
bool vis[N];
list<int> L;
int n,m;
void dfs(int u, bool ok){
	for(int i=0; i<v[u].size(); ++i){ 
		if(!vis[v[u][i]]){
			if(ok) L.push_front(v[u][i]);
			else L.push_back(v[u][i]);
			vis[v[u][i]] = true;
			dfs(e,ok);
			return;
		}
	}
}
int main(){
	scanf("%d%d",&n,&m);
	memset(vis,false,sizeof(vis));
	while(m--){
		int a,b;
		scanf("%d%d",&a,&b);
		v[a].push_back(b);
		v[b].push_back(a);
	}
	L.push_back(1);
	L.push_back(v[1][0]);
	vis[1]=vis[v[1][0]]=true;
	dfs(1,true);
	dfs(v[1][0], false);
	printf("%d\n",L.size());
	for(auto it=L.begin(); it!=L.end(); ++it)
		printf("%d ",*it);
	printf("\n");
	return 0;
}

Compiler output:
a.cc:38:2: error: stray '#' in program
   38 | }#include<bits/stdc++.h>
      |  ^
a.cc: In function 'void dfs(int, bool)':
a.cc:14:29: error: 'e' was not declared in this scope
   14 |                         dfs(e,ok);
      |                             ^
a.cc: At global scope:
a.cc:38:3: error: 'include' does not name a type
   38 | }#include<bits/stdc++.h>
      |   ^~~~~~~
a.cc:40:11: error: redefinition of 'const int N'
   40 | const int N = 1e5+3;
      |           ^
a.cc:3:11: note: 'const int N' previously defined here
    3 | const int N = 1e5+3;
      |           ^
a.cc:41:13: error: redefinition of 'std::vector<int> v [100003]'
   41 | vector<int> v[N];
      |             ^
a.cc:4:13: note: 'std::vector<int> v [100003]' previously declared here
    4 | vector<int> v[N];
      |             ^
a.cc:42:6: error: redefinition of 'bool vis [100003]'
   42 | bool vis[N];
      |      ^~~
a.cc:5:6: note: 'bool vis [100003]' previously declared here
    5 | bool vis[N];
      |      ^~~
a.cc:43:11: error: redefinition of 'std::__cxx11::list<int> L'
   43 | list<int> L;
      |           ^
a.cc:6:11: note: 'std::__cxx11::list<int> L' previously declared here
    6 | list<int> L;
      |           ^
a.cc:44:5: error: redefinition of 'int n'
   44 | int n,m;
      |     ^
a.cc:7:5: note: 'int n' previously declared here
    7 | int n,m;
      |     ^
a.cc:44:7: error: redefinition of 'int m'
   44 | int n,m;
      |       ^
a.cc:7:7: note: 'int m' previously declared here
    7 | int n,m;
      |       ^
a.cc:45:6: error: redefinition of 'void dfs(int, bool)'
   45 | void dfs(int u, bool ok){
      |      ^~~
a.cc:8:6: note: 'void dfs(int, bool)' previously defined here
    8 | void dfs(int u, bool ok){
      |      ^~~
a.cc: In function 'void dfs(int, bool)':
a.cc:51:29: error: 'e' was not declared in this scope
   51 |                         dfs(e,ok);
      |                             ^
a.cc: At global scope:
a.cc:56:5: error: redefinition of 'int main()'
   56 | int main(){
      |     ^~~~
a.cc:19:5: note: 'int main()' previously defined here
   19 | int main(){
      |     ^~~~