Dijkstra algorithm

++
#include <iostream>
#include <vector>
#include <unordered_set>

using namespace std;

template <typename T>
void print(const T& collection, const string& label="") {
  if (!label.empty()) {
    cout << label << ": ";
  }
  for (const auto& e : collection) {
    cout << e << " ";
  }
  cout << endl;
}

class Graph {
  struct Node {
    int id;
    int weight;
    Node(int id, int weight) : id(id), weight(weight) {}
  };
  struct Vertex {
    int distance = numeric_limits<int>::max();
    int previous = -1;
    unordered_set<Node> neighbours;
  };
  vector<Vertex> vertices;
  
public:
  Graph(int num_vertices): vertices(num_vertices) {}
  
  void add_edge(int u, int v, int weight) {