#include "longesttrip.h"
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
vi longest_trip(int n, int D)
{
random_start();
vi verts;
rep(i,n) verts.pb(i);
shuffle(all(verts),mt);
vi t1 = {verts[0]};
vi t2 = {verts[1]};
bool is_nc = 0;
rep2(i,2,n-1)
{
int v = verts[i];
if(los(0,1) == 0) swap(t1,t2);
if(are_connected({v},{t1.back()}))
{
t1.pb(v);
is_nc = 0;
}
else
{
if(is_nc)
{
is_nc = 1;
t2.pb(v);
}
else
{
if(are_connected({v},{t2.back()}))
{
is_nc = 1;
t2.pb(v);
}
else
{
for(int j = siz(t2)-1; j >= 0; j--)
{
t1.pb(t2[j]);
}
t2 = {v};
is_nc = 0;
}
}
}
}
vi ends1;
vi ends2;
if(siz(t1) == 1) ends1 = {t1[0]};
else ends1 = {t1[0],t1.back()};
if(siz(t2) == 1) ends2 = {t2[0]};
else ends2 = {t2[0],t2.back()};
if(are_connected(ends1,ends2))
{
if(are_connected(ends1,{ends2[0]}))
{
if(are_connected({ends1[0]},{ends2[0]}))
{
reverse(all(t1));
forall(it,t2) t1.pb(it);
return t1;
}
else
{
forall(it,t2) t1.pb(it);
return t1;
}
}
else
{
reverse(all(t2));
if(are_connected({ends1[0]},{ends2.back()}))
{
reverse(all(t1));
forall(it,t2) t1.pb(it);
return t1;
}
else
{
forall(it,t2) t1.pb(it);
return t1;
}
}
}
if(siz(t1) > siz(t2)) return t1;
return t2;
}
