#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    void allTopoSorts(vector<vector<int>>& adj, vector<int>& indegree,
                      vector<bool>& visited, vector<int>& curr, int V) {
        bool flag = false;

        for (int i = 0; i < V; i++) {
            if (!visited[i] && indegree[i] == 0) {
                // choose this node
                visited[i] = true;
                curr.push_back(i);

                // reduce indegree of neighbors
                for (int nbr : adj[i]) indegree[nbr]--;

                // recurse
                allTopoSorts(adj, indegree, visited, curr, V);

                // backtrack
                visited[i] = false;
                curr.pop_back();
                for (int nbr : adj[i]) indegree[nbr]++;

                flag = true;
            }
        }

        // if no node was picked -> we found one valid order
        if (!flag) {
            for (int x : curr) cout << x << " ";
            cout << "\n";
        }
    }

    void findAllTopologicalSorts(int V, vector<vector<int>>& edges) {
        vector<vector<int>> adj(V);
        vector<int> indegree(V, 0);

        for (auto& e : edges) {
            adj[e[0]].push_back(e[1]);
            indegree[e[1]]++;
        }

        vector<bool> visited(V, false);
        vector<int> curr;
        allTopoSorts(adj, indegree, visited, curr, V);
    }
};

int main() {
    int V = 4;
    vector<vector<int>> edges = {
        {0, 1}, {0, 2}, {1, 3}, {2, 3}
    };

    Solution s;
    cout << "All possible Topological Sorts:\n";
    s.findAllTopologicalSorts(V, edges);

    return 0;
}