Task B Gym 100165

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <map>
#include <set>
#include <vector>
#include <algorithm>
#include <queue>
#include <bitset>
#include <stack>
#include <iostream>
#include <fstream>
#include <cmath>

#define sqr(a) ((a)*(a))
#define odd(a) ((a)&1)
#define foru(i,n) for (int i=0;i<(n);i++)
#define ford(i,n) for (int i=(n)-1;i>=0;i--)
#define forab(i,l,r) for (int i=(l);i<=(r);i++)
#define forabd(i,r,l) for (int i=(r);i>=(l);i--)
#define pb push_back
#define F first
#define S second
#define all(x) x.begin(),x.end()
#define sz(__X) (int)__X.size()
#define pii pair<int,int>
#define pb push_back
#define mp make_pair

const double eps=1e-19;
const double PI=acos(-1.0);
const int INF=1000*1000*1000+7;
const int MAXN = 200005;

using namespace std;

int n,m;
vector<int> g[MAXN];
int col[MAXN];
int pr[MAXN];
vector<int> ans;
vector<int> now;
int cicl_st, cicl_end;

void update_ans()
{
    now.clear();
    for (int v=cicl_st; v!=cicl_end; v=pr[v])
        now.pb(v);
    now.pb(cicl_end);
    if (sz(now)>sz(ans))
    {
        ans.clear();
        ans.assign( all(now) );
    }
}

void dfs(int v, int pred)
{
    col[v] = 1;
    for (int j=0; j<sz(g[v]); j++)
    {
        int u=g[v][j];
        if (u==pred) continue;
        if (col[u]==0)
        {
            pr[u] = v;
            dfs(u, v);
        }
        else if (col[u]==1)
        {
            cicl_end = u; cicl_st=v;
            update_ans();
        }
    }
    col[v]=0;
}

int main()
{
    freopen("doggy.in", "r", stdin);
    freopen("doggy.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for (int i=0; i<m; i++)
    {
        int v,u;
        scanf("%d %d", &v, &u);
        v--;u--;
        g[v].pb(u);
        g[u].pb(v);
    }
    ans.pb(0);
    dfs(0, -1);
    printf("%d\n", sz(ans));
    for (int i=0; i<sz(ans); i++)
        printf("%d ", ans[i]+1);
    return 0;
}