ИИ - Алгоритми 2021 задачи за решавање: Суперхерој

#include <bits/stdc++.h>
using namespace std;
struct vertex // one point from the vector
{
    vector <int> edges_connected;
    bool visited;
    int far_from_start;
    vertex()
    {
        visited = false;
        far_from_start = -1;
        edges_connected.erase(edges_connected.begin(), edges_connected.end());
        return;
    }
};
int main()
{
    int vertices, edges, start_index, end_index;
    cin >> vertices >> edges;
    vector <vertex> buildings(vertices + 2); // the vector
    for (int i = 0; i < edges; i++) // entering edges
    {
        int a, b;
        cin >> a >> b;
        buildings[a].edges_connected.push_back(b);
        buildings[b].edges_connected.push_back(a);
    }
    cin >> start_index >> end_index;
    queue <int> bfs_queue; // the queue for BFS
    bfs_queue.push(start_index); // add the start point
    buildings[start_index].visited = true;
    buildings[start_index].far_from_start = 0;
    while (!bfs_queue.empty()) // BFS
    {
        int building = bfs_queue.front(); // the vertex index
        bfs_queue.pop();
        if (building == end_index) // found a way
        {
            cout << buildings[building].far_from_start; // return how far from start is the building
            return 0;
        }
        for (int i = 0; i < buildings[building].edges_connected.size(); i++) // check all connected vertices
        {
            if (!buildings[buildings[building].edges_connected[i]].visited) // if vertex is not checked
            {
                buildings[buildings[building].edges_connected[i]].visited = true; // check this vertex
                buildings[buildings[building].edges_connected[i]].far_from_start = buildings[building].far_from_start + 1;
                bfs_queue.push(buildings[building].edges_connected[i]); // add vertex to BFS queue
            }
        }
    }
    cout << 0; // cannot find a way
    return 0;
}