Implementación de un Grafo con Matrices e incluye método para buscar alcance mínimo a otros vértices

Graph_class.cpp

class Graph {
    private:
        int **G;
        int size;
    public:
        Graph(int n) {
            n++;
            G = new int*[n];
            for (int i = 0; i < n; i++) {
                G[i] = (int*)calloc(n, sizeof(int));
                // G[i] = new int[n];
            }
            this->size = n;
        }
        ~Graph() {
            for (int i = 0; i < this->size; i++) {
                delete G[i];
            }
            delete G;
        }
        void showGraph() {
            cout << "      \t";
            for (int i = 0; i < this->size; i++) {
                cout << i << "\t";
            }
            cout << endl;
            cout << "      \t";
            for (int i = 0; i < this->size; i++) {
                cout << "=\t";
            }
            cout << endl;
            for (int i = 0; i < this->size; i++) {
                cout << "i = " << i << "\t";
                for (int j = 0; j < this->size; j++) {
                    cout << G[i][j] << "\t";
                }
                cout << endl;
            }
        }
        void add_edge(int u, int v) {
            G[u][v] = G[v][u] = 1;
        }

        vector<int> shortest_reach(int start) {
            // this->showGraph();
            queue< int > q;
            vector<int> nodes(this->size, 0);
            q.push(start);
            nodes[start] = 1;
            int u;
            while (!q.empty()) {
                u = q.front();
                q.pop();
                for (int v = 1; v < this->size; v++) {
                    if (G[u][v] && !nodes[v]) {
                        nodes[v] = nodes[u] + 1;
                        q.push(v);
                    }
                }
            }
            return nodes;
        }

};