D. Choosing Capital for Treeland

// Problem: D. Choosing Capital for Treeland
// Contest: Codeforces - Codeforces Round #135 (Div. 2)
// URL: https://codeforces.com/contest/219/problem/D
// Memory Limit: 256 MB
// Time Limit: 3000 ms
// Parsed on: 14-08-2021 16:23:09 IST (UTC+05:30)
// Author: Kapil Choudhary
// ********************************************************************
// कर्मण्येवाधिकारस्ते मा फलेषु कदाचन |
// मा कर्मफलहेतुर्भूर्मा ते सङ्गोऽस्त्वकर्मणि || १.४७ ||
// ********************************************************************

#include<bits/stdc++.h>
using namespace std;

#define ll long long
#define ld long double
#define ull unsigned long long
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define F first
#define S second
#define PI 3.1415926535897932384626
#define sz(x) ((int)(x).size())

typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ull> vull;
typedef vector<bool> vb;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef vector<vull> vvull;
typedef vector<vb> vvb;
typedef vector<vc> vvc;
typedef vector<vs> vvs;

/************************************************** DEBUGGER *******************************************************************************************************/

#ifndef ONLINE_JUDGE
#define debug(x) cerr << #x <<" "; _print(x); cerr << endl;
#else
#define debug(x)
#endif

void _print(ll t) { cerr << t; }
void _print(int t) { cerr << t; }
void _print(string t) { cerr << t; }
void _print(char t) { cerr << t; }
void _print(ld t) { cerr << t; }
void _print(double t) { cerr << t; }
void _print(ull t) { cerr << t; }

template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);
template <class T> void _print(vector <vector<T>> v);
template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);
template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) { cerr << "{"; _print(p.F); cerr << ","; _print(p.S); cerr << "}"; }
template <class T> void _print(vector <T> v) { cerr << "[ "; for (T i : v) {_print(i); cerr << " "; } cerr << "]"; }
template <class T> void _print(vector <vector<T>> v) { cerr << "==>" << endl; for (vector<T> vec : v) { for(T i : vec) {_print(i); cerr << " "; } cerr << endl; } }
template <class T> void _print(set <T> v) { cerr << "[ "; for (T i : v) {_print(i); cerr << " "; } cerr << "]"; }
template <class T> void _print(multiset <T> v) { cerr << "[ "; for (T i : v) {_print(i); cerr << " "; } cerr << "]"; }
template <class T, class V> void _print(map <T, V> v) { cerr << "[ "; for (auto i : v) {_print(i); cerr << " "; } cerr << "]"; }

/*******************************************************************************************************************************************************************/

mt19937_64 rang(chrono::high_resolution_clock::now().time_since_epoch().count());
int rng(int lim) {
    uniform_int_distribution<int> uid(0,lim-1);
    return uid(rang);
}

const int INF = 0x3f3f3f3f;
const int mod = 1e9+7;

ll mod_exp(ll a, ll b) { a %= mod; if(a == 0) return 0LL; ll res = 1LL;
                         while(b > 0) { if(b & 1) res = (res * a) % mod; a = (a * a) % mod; b >>= 1; } return res; }

ll mod_inv(ll a) { return mod_exp(a, mod - 2); } // works only for prime value of "mod"
ll GCD(ll a, ll b) { return (b == 0) ? a : GCD(b, a % b); }

/******************************************************************************************************************************/

vector<vpii> g;

// dp_down[i] = #edges which are directed downwards in the path from 1 to i
// dp_up[i] = #edges which are directed upwards in the path from 1 to i
vi dp_down, dp_up;

// n = #nodes, upwards = total #edges directed up
int n, upwards;

void dfs(int cur, int par) {
    for(auto x: g[cur]) {
        int node = x.F, dir = x.S;
        if(node == par) continue;

        if(dir == 1) dp_down[node] = dp_down[cur] + 1;
        else dp_down[node] = dp_down[cur];

        if(dir == -1) dp_up[node] = dp_up[cur] + 1;
        else dp_up[node] = dp_up[cur];

        if(dir == -1) upwards += 1;

        // calculate value for child nodes
        dfs(node, cur);
    }
}

// https://www.youtube.com/watch?v=lrWshOTKaec&list=PLzVLIdIx9dQxCKaiktxELrtXtnItgAAIr&index=5
// https://codeforces.com/blog/entry/5160
void solve()
{
    cin >> n;

    g.clear(); g.resize(n + 1);
    dp_down.clear(); dp_down.resize(n + 1, 0);
    dp_up.clear(); dp_up.resize(n + 1, 0);
    upwards = 0;

    for(int i = 1; i < n; i++) {
        int x, y; cin >> x >> y;

        // 1 is for downward edge & -1 is for upward edge
        g[x].pb({y, 1});
        g[y].pb({x, -1});
    }

    dfs(1, 0);

    vi val(n + 1, 0);
    for(int i = 1; i <= n; i++) {
        val[i] = dp_down[i] + (upwards - dp_up[i]);
    }

    int mn = *min_element(val.begin() + 1, val.end());

    cout << mn << "\n";
    for(int i = 1; i <= n; i++) {
        if(val[i] == mn) cout << i << " ";
    }

    cout << "\n";
}

int main()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    srand(chrono::high_resolution_clock::now().time_since_epoch().count());

    // #ifndef ONLINE_JUDGE
    //     freopen("input.txt", "r", stdin);
    //     freopen("output.txt", "w", stdout);
    // #endif

    // #ifndef ONLINE_JUDGE
    //      freopen("error.txt", "w", stderr);
    // #endif

    int t = 1;
    // int test = 1;
    // cin >> t;
    while(t--) {
        // cout << "Case #" << test++ << ": ";
        solve();
    }

    return 0;
}