bfs.cpp

#include <bits/stdc++.h>

using namespace std;

vector<bool> v;
vector<vector<int>> g;

void func(int a, int b)
{
    g[a].push_back(b);
}
void bfs(int u)
{
    queue<int> q;

    q.push(u);
    v[u] = true;

    while (!q.empty())
    {

        int f = q.front();
        q.pop();

        cout << f << " ";

                for (auto i = g[f].begin(); i != g[f].end(); i++)
        {
            if (!v[*i])
            {
                q.push(*i);
                v[*i] = true;
            }
        }
    }
}

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

    v.assign(n, false);
    g.assign(n, vector<int>());

    int a, b;
    for (int i = 0; i < e; i++)
    {
        cin >> a >> b;
        func(a, b);
    }

    for (int i = 0; i < n; i++)
    {
        if (!v[i])
            bfs(i);
    }

    return 0;
}