обход в ширину

#include <bits/stdc++.h>

using namespace std;

int n, a, b, pr[5000], dist[5000], p[5000], ans;
vector <int> x[5000];
queue <int> q;
int main(){
 cin >> n;
 for(int i = 1; i <= n; i++){
   for(int j = 1; j <= n; j++){
     cin >> a;
     if(a){
       x[i].push_back(j);
       x[j].push_back(i);
     }
   }
 }
 cin >> a >> b;
 q.push(a);
 pr[a] = 1;
 dist[a] = 0;
 p[a] = -1;

 while(!q.empty()){
   int v = q.front();
   q.pop();
   for(int i = 0; i < x[v].size(); i++){
     int to = x[v][i];
     if(!pr[to]){
       pr[to] = 1;
       q.push(to);
       dist[to] = dist[v] + 1;
       p[to] = v;
     }
   }
 }
 if(!pr[b]){
   cout << -1;
 }
 else{
   vector <int> path;
   for(int i = b; i != -1; i = p[i]){
      path.push_back(i);
      ans++;
   }
   reverse(path.begin(), path.end());
   if(ans - 1){
     cout << ans - 1 << endl;
    for(int i = 0; i < path.size(); i++){
      cout << path[i] << " ";
    }
   }
   else{
     cout << ans - 1;
   }
 }
}