Dijkstra implementation C++

#include <algorithm>
#include <iostream>
#include <queue>
#include <utility>
#include <vector>

using namespace std;

#define DISTANCE_INITIALIZATION_VALUE -1

void add_edge_directed(vector<vector<pair<long long, long long>>> &G,
                       long long u, long long v, long long weight) {
  G.at(u).push_back(make_pair(v, weight));
  // G.at(v).push_back(make_pair(u, weight));
}

class Compare {
 public:
  // Ringraziamo l'umile dipendente cicciottello
  // per aver scoperto la necessitá di una inspiegabile parentesi tonda
  bool operator()(pair<long long, long long> &lhs,
                  pair<long long, long long> &rhs) {
    return lhs.second > rhs.second;
  }
};

int main() {
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);

  long long V, E;
  cin >> V >> E;
  vector<vector<pair<long long, long long>>> G(V, vector<pair<long long, long long>>());

  long long source, destination;
  cin >> source >> destination;
  // Per gli indici che partono da 1
  // source--;
  // destination--;

  for (long long edge = 0; edge < E; edge++) {
    long long u, v, w;
    cin >> u >> v >> w;
    // Per gli indici che partono da 1
    // u--;
    // v--;
    add_edge_directed(G, u, v, w);
  }

  // Shortest path
  priority_queue<pair<long long, long long>, vector<pair<long long, long long>>, Compare> queue;

  queue.push(make_pair(source, 0));

  vector<bool> visited(V, false);
  vector<long long> distances(V, DISTANCE_INITIALIZATION_VALUE);

  while (!queue.empty()) {
    pair<long long, long long> curr = queue.top();
    queue.pop();

    if (!visited.at(curr.first)) {
      visited.at(curr.first) = true;
      distances.at(curr.first) = curr.second;

      for (pair<long long, long long> neighbour : G.at(curr.first)) {
        if (!visited.at(neighbour.first)) {
          queue.push(
              make_pair(neighbour.first, curr.second + neighbour.second));
        }
      }
    }
  }

  cout << distances.at(destination);
  return 0;
}