DFS

#include <iostream>

using namespace std;

const int N = 100010, M = 100010;

int n, m;

struct Node
{
    int id;
    Node* next;
    Node(int _id): id(_id), next(NULL){}
}*head[N];

bool st[N];

void add(int a, int b)
{
    auto p = new Node(b);
    p->next = head[a];
    head[a] = p;
}

void dfs(int u)
{
    st[u] = true;
    cout << u << " ";
    for(auto q = head[u]; q; q = q->next)
    {
        int j = q->id;
        if(!st[j]) dfs(j);
    }
}

int main()
{
    cin >> n >> m;

    while(m --)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }

    for(int i = 1; i <= n; i ++)
        if(!st[i]) dfs(i);

    return 0;
}

BFS

#include <iostream>
#include <queue>
using namespace std;

const int N = 100010, M = 100010;

int n, m;

struct Node
{
    int id;
    Node* next;
    Node(int _id): id(_id), next(NULL){}
}*head[N];

bool st[N];

void add(int a, int b)
{
    auto p = new Node(b);
    p->next = head[a];
    head[a] = p;
}

void bfs()
{
    queue <int> q;
    q.push(1);
    st[1] = true;

    while(q.size())
    {
        auto t = q.front();
        q.pop();
        cout << t << " ";
        for(auto p = head[t]; p; p = p->next)
        {
            int j = p->id;
            if(!st[j])
            {
                st[j] = true;
                q.push(j);
            }
        }
    }

}

int main()
{
    cin >> n >> m;

    while(m --)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }

    bfs();

    return 0;
}