func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long LL_MIN = std::numeric_limits<long long>::min();   const long long LL_MAX = std::numeric_limits<long long>::max();   template <class T, class R>   ostream& operator<<(ostream& o, const pair<T, R>& p) {     o <<  (  << p.first <<  ,   << p.second <<  ) ;     return o;   }   template <class T, class R>   istream& operator>>(istream& o, pair<T, R>& p) {     o >> p.first >> p.second;     return o;   }   template <class T>   string to_string(const T& x) {     stringstream o;     o <<  [ ;     for (__typeof((x).begin()) i = ((x).begin()); i != (x).end(); ++i) {       o << ((i != x.begin()) ?  ,   :   ) << *i;     }     o <<  ] ;     string r;     getline(o, r);     return r;   }   template <class T>   T get_next(string& s) {     stringstream ss(s);     T r;     ss >> r;     getline(ss, s);     return r;   }   template <class T>   void split_string(const string& s, vector<T>& o) {     stringstream ss(s);     o.clear();     T x;     while (ss >> x) {       o.push_back(x);     }   }   void trim(string& s) {     stringstream ss;     ss << s;     s.clear();     ss >> s;   }   template <class T, class R>   ostream& operator<<(ostream& o, const map<T, R>& x) {     o << to_string(x);     return o;   }   template <class T>   ostream& operator<<(ostream& o, const vector<T>& x) {     o << to_string(x);     return o;   };   template <class T>   ostream& operator<<(ostream& o, const set<T>& x) {     o << to_string(x);     return o;   };   template <class T>   ostream& operator<<(ostream& o, const deque<T>& x) {     o << to_string(x);     return o;   };   const long long INFL = 1000000000LL * 1000000000LL + 1000LL;   const int INF = 1000000000 + 1000;   const long long MOD = 1000000009;   struct Tri {     int a, b, c;     Tri(int a, int b, int c) : a(a), b(b), c(c) {}   };   queue<Tri> q;   int n, m, a, b;   vector<int> graf[510];   bool sol[510][510][2];   int dist[510][510][2], f[510][510][2];   int main() {     scanf( %d %d , &n, &m);     for (int i = 1; i <= m; i++) {       scanf( %d %d , &a, &b);       graf[a].push_back(b);       graf[b].push_back(a);     }     dist[1][n][0] = 0;     q.push(Tri(1, n, 0));     sol[1][n][0] = true;     while (q.size()) {       Tri t = q.front();       q.pop();       if (t.c == 0) {         for (__typeof((graf[t.a]).begin()) a = ((graf[t.a]).begin());              a != (graf[t.a]).end(); ++a) {           if (!sol[*a][t.b][1]) {             sol[*a][t.b][1] = true;             dist[*a][t.b][1] = dist[t.a][t.b][0] + 1;             q.push(Tri(*a, t.b, 1));             f[*a][t.b][1] = t.a;           }         }       } else {         for (__typeof((graf[t.b]).begin()) b = ((graf[t.b]).begin());              b != (graf[t.b]).end(); ++b) {           if (!sol[t.a][*b][0] && t.a != *b) {             sol[t.a][*b][0] = true;             dist[t.a][*b][0] = dist[t.a][t.b][1];             q.push(Tri(t.a, *b, 0));             f[t.a][*b][0] = t.b;           }         }       }     }     if (!sol[n][1][0]) {       printf( -1 n );     } else {       printf( %d n , dist[n][1][0]);       a = n;       b = 1;       vector<int> ra, rb;       ra.push_back(n);       rb.push_back(1);       while (make_pair(a, b) != make_pair(1, n)) {         rb.push_back(f[a][b][0]);         b = f[a][b][0];         ra.push_back(f[a][b][1]);         a = f[a][b][1];       }       for (__typeof((rb).begin()) it = ((rb).begin()); it != (rb).end(); ++it) {         printf( %d  , *it);       }       printf(  n );       for (__typeof((ra).begin()) it = ((ra).begin()); it != (ra).end(); ++it) {         printf( %d  , *it);       }       printf(  n );     }   }   