LEXIPATH (lqdoj) - DFS

// https://lqdoj.edu.vn/problem/lexipath
#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 5;

vector<int> g[N];
bool visited[N];

int n, m, s, t;
vector<int> path;

// DFS(x) == true nếu x == t hoặc DFS(con của x) == t
bool DFS(int u) {
    visited[u] = true;

    if (u == t) {
        path.push_back(u);
        return true;
    }

    for (int v : g[u]) {
        if (!visited[v] && DFS(v) == true) {
            path.push_back(u);
            return true;
        }
    }

    return false;
}

int main() {
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
#else
    freopen("LEXIPATH.inp", "r", stdin);
    freopen("LEXIPATH.out", "w", stdout);
#endif
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> n >> m >> s >> t;

    for (int i = 1; i <= m; i++) {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
    }

    for (int i = 1; i <= n; i++) {
        sort(g[i].begin(), g[i].end());
    }

    DFS(s);

    for (int i = (int) path.size() - 1; i >= 0; i--) {
        cout << path[i] << ' ';
    }

    return 0;
}