1vector<vector<int>> adj;  // adjacency list representation
2int n; // number of nodes
3int s; // source vertex
4
5queue<int> q;
6vector<bool> used(n);
7vector<int> d(n), p(n);
8
9q.push(s);
10used[s] = true;
11p[s] = -1;
12while (!q.empty()) {
13    int v = q.front();
14    q.pop();
15    for (int u : adj[v]) {
16        if (!used[u]) {
17            used[u] = true;
18            q.push(u);
19            d[u] = d[v] + 1;
20            p[u] = v;
21        }
22    }
23}
24