bfs_traversal_with_level_tracking.cpp

#include <bits/stdc++.h>
using namespace std;

vector<int> v[1005];
bool vis[1005];
int level[1005];

void bfs(int src)
{
    queue<int> q;
    q.push(src);
    vis[src] = true;
    level[src] = 0;

    while (!q.empty())
    {
        int front = q.front();
        q.pop();

        cout << front << endl;

        for (int child : v[front])
        {
            if (!vis[child])
            {
                q.push(child);
                vis[child] = true;
                level[child] = level[front] + 1;
            }
        }
    }
}

int main()
{
    int n, e;
    cin >> n >> e;

    while (e--)
    {
        int a, b;
        cin >> a >> b;

        v[a].push_back(b);
        v[b].push_back(a);
    }

    memset(vis, false, sizeof(vis));
    memset(level, -1, sizeof(level));

    int src;
    cin >> src;
    bfs(src);

    cout << endl
         << "Level of Nodes: " << endl;
    for (int i = 0; i < n; i++)
    {
        cout << i << " -> " << level[i] << endl;
    }

    return 0;
}