有遍历顺序，从小到大

图的bfs

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int n, m;
const int N = 100010;

int h[N], e[N], ne[N], idx;

void add(int a, int b)  // 添加一条边a->b
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

int q[N], d[N];
vector<int> ans;

int bfs()
{
    int hh = 0, tt = -1;
    memset(d, -1, sizeof d);
    d[1] = 0;
    q[++ tt] = 1;
    ans.push_back(1);
    while (hh <= tt)
    {
        int t = q[hh ++];
        vector<int> p;
        for (int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];

            if (d[j] == -1)
            {
                p.push_back(j);
            }
        }
        sort(p.begin(), p.end());
        for (int i = 0; i < p.size(); i ++)
        {
            ans.push_back(p[i]);
            d[p[i]] = d[t] + 1;
            q[++ tt] = p[i];
        }

    }
    return d[n];
}


int main()
{
    cin >> n >> m;
    memset(h, -1, sizeof h);

    while (m --)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }
    int t = bfs();
    if (t == -1)
    {
        return -1;
    }
    else
    {
        for (int i = 0; i < n; i++ )
        {
            cout << ans[i] << ' ';
        }

    }
    return 0;
}

图的dfs

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;
const int N = 100010;
int n, m;

int h[N], e[N], ne[N], idx;

void add(int a, int b)  // 添加一条边a->b
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

bool st[N];

vector<int> res;

void dfs(int u)
{
    if (st[u])
        return ;
    res.push_back(u);
    st[u] = true;
    vector<int> p;
    for (int i = h[u]; i != -1; i = ne[i])
    {
        int j = e[i];
        if (!st[j])
        {
            p.push_back(j);
        }
    }
    sort(p.begin(), p.end());
    for (int i = 0; i < p.size(); i++)
    {
        dfs(p[i]);
    }
    return ;
}


int main()
{
    memset(h, -1, sizeof h);

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

    dfs(1);
    if (res.size() != n)
    {
        return -1;
    }
    else
    {
        for (int i = 0; i < res.size(); i++)
        {
            cout << res[i] << ' ';
        }
    }

    return 0;
}