https://www.luogu.com.cn/problem/P5318

#include<iostream>
#include<vector>
#include<queue>
using namespace std;
const int MAXN = 100005;
int n, m;
vector<int>p[MAXN];
vector<int>k[MAXN];
queue<int>q;
bool u[MAXN];
bool w[MAXN];
void solve(int x) {
	cout << x << " ";
	for (int i = 0, sz = k[x].size(); i < sz; i++) {
		if (!w[p[x][i]]) {
			w[p[x][i]] = true;
			solve(k[x][i]);
		}
	}
}
int main() {
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		int x, y;
		cin >> x >> y;
		p[x].push_back(y);
		k[x].push_back(y);
	}
	w[1] = true;
	u[1] = true;
	q.push(1);
	solve(1);
	cout << endl;
	while (!q.empty()) {
		int x = q.front();
		q.pop();
		cout << x << " ";
		for (int i = 0, sz = p[x].size(); i < sz; i++) {
			if (!u[p[x][i]]) {
				u[p[x][i]] = true;
				q.push(p[x][i]);
			}
		}
	}
	return 0;
}