Message Route

#include <bits/stdc++.h>

using namespace std;

struct Comp{
    int v;
    vector<int> route;
};

int n, m;
vector<int> link[100001];
queue<Comp> q;
bool visited[100001];

int main(){
    //freopen("message.in", "r", stdin);

    cin >> n >> m;
    int a, b;
    for(int i=0; i<m; i++){
        cin >> a >> b;
        link[a].push_back(b);
        link[b].push_back(a);
    }
    vector<int> r;
    r.push_back(1);
    q.push({1, r});
    visited[1] = true;
    while(!q.empty()){
        Comp cur = q.front();
        q.pop();
        if(cur.v == n){
            cout << cur.route.size() << '\n';
            string p = "";
            //int ans = 1;
            for(int i=0; i<cur.route.size(); i++){
                //if(cur.route[i] == ' ') ans++;
                cout << p << cur.route[i];
                p = " ";
            }
            //cout << ans << '\n';
            //cout << cur.route << '\n';
            cout << '\n';
            return 0;
        }
        for(auto v: link[cur.v]){
            if(!visited[v]){
                visited[v] = true;
                cur.route.push_back(v);
                //cout << cur.route << '\n';
                q.push({v, cur.route});
                cur.route.pop_back();
                //!!!use vector because saves a lot of run time instead of string
                //visited[v] = false;
                //do not need to turn visited back because it will cause double check which is not needed
            }
        }
    }
    cout << "IMPOSSIBLE" << '\n';

    return 0;
}