1+ #include < bits/stdc++.h>
2+ 3+ using namespace std ;
4+ 5+ typedef long int li;
6+ typedef long long int lli;
7+ typedef vector<long long int > vlli;
8+ typedef vector<int > vi;
9+ typedef stack<long long int > slli;
10+ typedef pair<lli, lli> plli;
11+ 12+ class Graph
13+ {
14+ 15+ vector<vector<lli>> adj;
16+ lli nodes;
17+ vector<bool > visited;
18+ vector<lli> path;
19+ lli pre ;
20+ 21+ public:
22+ Graph (lli nodes)
23+ {
24+ this ->adj .resize (nodes, vector<lli>{});
25+ this ->nodes = nodes;
26+ this ->visited .resize (nodes, false );
27+ }
28+ 29+ void addDirectedEdge (lli src, lli dst)
30+ {
31+ 32+ if (src == dst)
33+ {
34+ return ;
35+ }
36+ 37+ this ->adj [src].emplace_back (dst);
38+ }
39+ 40+ void addUndirectedEdge (lli src, lli dst)
41+ {
42+ 43+ if (src == dst)
44+ {
45+ return ;
46+ }
47+ 48+ this ->adj [src].emplace_back (dst);
49+ this ->adj [dst].emplace_back (src);
50+ }
51+ 52+ bool dfs (lli node, lli parent)
53+ {
54+ 55+ this ->visited [node] = true ;
56+ 57+ this ->path .push_back (node);
58+ 59+ for (auto neighbour : this ->adj [node])
60+ {
61+ 62+ if (!this ->visited [neighbour])
63+ {
64+ 65+ if (dfs (neighbour, node))
66+ {
67+ return true ;
68+ }
69+ }
70+ else if (neighbour != parent)
71+ {
72+ 73+ this ->path .push_back (neighbour);
74+ this ->pre = neighbour;
75+ return true ;
76+ }
77+ }
78+ 79+ this ->path .pop_back ();
80+ return false ;
81+ }
82+ 83+ void searchRoundTrips ()
84+ {
85+ 86+ bool flag = false ;
87+ 88+ for (lli i = 0 ; i < this ->nodes ; i++)
89+ {
90+ 91+ if (!this ->visited [i])
92+ {
93+ 94+ if (this ->dfs (i, -1 ))
95+ {
96+ 97+ flag = true ;
98+ break ;
99+ }
100+ }
101+ }
102+ 103+ if (flag)
104+ {
105+ 106+ lli j = 0 ;
107+ 108+ for (j = 0 ; j < this ->path .size (); j++)
109+ {
110+ 111+ if (this ->path [j] == this ->pre )
112+ {
113+ break ;
114+ }
115+ }
116+ 117+ cout << this ->path .size () - j << ' \n '
118+ 119+ for (lli i = j; i < this ->path .size (); i++)
120+ {
121+ 122+ cout << this ->path [i] + 1 << ' '
123+ }
124+ 125+ cout << ' \n '
126+ }
127+ else
128+ {
129+ 130+ cout << " IMPOSSIBLE\n "
131+ }
132+ }
133+ };
134+ 135+ void task ()
136+ {
137+ lli cities, roads;
138+ cin >> cities >> roads;
139+ Graph g (cities);
140+ lli a, b;
141+ for (lli i = 0 ; i < roads; i++)
142+ {
143+ cin >> a >> b;
144+ g.addUndirectedEdge (a - 1 , b - 1 );
145+ }
146+ 147+ g.searchRoundTrips ();
148+ }
149+ 150+ int main ()
151+ {
152+ 153+ ios::sync_with_stdio (0 );
154+ cin.tie (0 );
155+ 156+ task ();
157+ 158+ return 0 ;
159+ }
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