Shared code

#include<bits/stdc++.h>
using namespace std;
vector<int> adj[200005];
vector<int> visited;
vector<int> par;
vector<int> dist;
pair<int,int> dfs(int src){
    visited[src] = 1;
    for(auto n : adj[src]){
        if(n == par[src]) continue;
        if(visited[n] == 0){
            par[n] = src;
            dist[n] = dist[src] + 1;
            pair<int,int> cycle = dfs(n);
            if(cycle.first != -1 && cycle.second != -1) 
                return cycle;
        }
        else{
            if(dist[src] - dist[n] + 1 > 2){
                return {n , src};
            }
        }
    }
    return {-1,-1};
}
void print_path(int src, int node1, int node2){
    int distinct_nodes = dist[node2] - dist[node1] + 1;
    int curr_node = node2;
    cout << distinct_nodes << endl;
    while(curr_node != par[node1]){
        cout << curr_node << " ";
        curr_node = par[curr_node];
    }
    cout << node2;
    exit(0);
}
int main(){
    int n, m;
    cin >> n >> m;
    for(int i = 0; i < m; ++i){
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    visited.resize(n + 1, 0);
    par.resize(n + 1, 0);
    dist.resize(n + 1, 0);
    for(int i = 0; i < n; ++i){
        if(visited[i] == 0){
            auto cycle = dfs(i + 1);
            if(cycle.first != -1 && cycle.second != -1){
                print_path(i, cycle.first, cycle.second);
            }
        }
    }
    cout << "IMPOSSIBLE";
    return 0;
}