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message routes.cpp
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message routes.cpp
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#include<iostream>
#include<vector>
#include<bits/stdc++.h>
#define lli long long int
#define mod 1000000007
#define pb push_back
#define mk make_pair
#define fastio ios_base::sync_with_stdio(false); cout.tie(NULL);
using namespace std;
vector<int> ar[100001];
int main()
{
fastio;
int n,m,a,b,i;
cin>>n>>m;
int path[n+1]={0};
for(i=0;i<m;i++)
{
cin>>a>>b;
ar[a].pb(b);
ar[b].pb(a);
}
queue<int> q;
q.push(1);
path[1]=-1;
while(!q.empty())
{
int cur=q.front();
q.pop();
if(cur==n)
break;
for(auto child : ar[cur])
{
if(path[child]==0)
{
path[child]=cur;
q.push(child);
}
}
}
if(path[n]==0)
cout<<"IMPOSSIBLE";
else
{
i=n;
vector<int> ans;
while(path[i]!=-1)
{
ans.pb(i);
i=path[i];
}
ans.pb(1);
reverse(ans.begin(),ans.end());
cout<<ans.size()<<"\n";
for(auto el : ans)
cout<<el<<" ";
}
return 0;
}