Single Source Shortest Path.cpp

//AnkitCode99 here....
#include<bits/stdc++.h>
#define endl "\n"
typedef long long int ll;
#define MOD 1000000007
#define mp make_pair
#define pll pair<ll,ll>
#define pb push_back
//max xor btw range of two numbers..
#define max_XOR(a,b) (1 << int(log2(a ^ b) + 1)) - 1
#define vl vector<ll>
#define inf ll(1e20)
#define all(v) v.begin(),v.end()
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define rep(i,a,b) for(long long int i=a;i<b;i++)
#define nrep(i,a,b) for(long long int i=a;i>=b;i--)
#define ceil(a,b) a/b+((a%b ==0 )?0:1)
using namespace std;

const ll sz=100005;
vl ar[sz];
ll dist[sz];
ll par[sz];
bool vis[sz];

void dfs(ll node,ll dis,ll p)
{
	par[node]=p;
	vis[node]=true;
	dist[node]=dis;
	for(ll child:ar[node])
	{
		if(!vis[child])
		{
			dfs(child,dist[node]+1,node);
		}
	}
}

int main()
{
	fast;
 //    #ifndef ONLINE_JUDGE
	// freopen("IP.txt","r",stdin);
	// freopen("OP.txt","w",stdout);
	// #endif
	//n=number of nodes, m=number of edges
	ll n,m;
	cin>>n>>m;

	rep(i,0,m)
	{
		ll a,b;
		cin>>a>>b;
		ar[a].pb(b);
		ar[b].pb(a);
	}

	dfs(1,0,-1);

	if(!vis[n])
		cout<<"IMPOSSIBLE";
	else
	{
		ll curr=n;
		vl path;

		while(curr!=-1)
		{
			path.pb(curr);
			curr=par[curr];
		}

		reverse(all(path));
		cout<<path.size()<<"\n";
		for(auto x:path)
			cout<<x<<" ";
	}
}