<p>There are&nbsp;<code>n</code>&nbsp;items each&nbsp;belonging to zero or one of&nbsp;<code>m</code>&nbsp;groups where <code>group[i]</code>&nbsp;is the group that the <code>i</code>-th item belongs to and it&#39;s equal to <code>-1</code>&nbsp;if the <code>i</code>-th item belongs to no group. The items and the groups are zero indexed. A group can have no item belonging to it.</p>

<p>Return a sorted list of the items such that:</p>

<ul>
	<li>The items that belong to the same group are next to each other in the sorted list.</li>
	<li>There are some&nbsp;relations&nbsp;between these items where&nbsp;<code>beforeItems[i]</code>&nbsp;is a list containing all the items that should come before the&nbsp;<code>i</code>-th item in the sorted array (to the left of the&nbsp;<code>i</code>-th item).</li>
</ul>

<p>Return any solution if there is more than one solution and return an <strong>empty list</strong>&nbsp;if there is no solution.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><strong><img alt="" src="https://assets.leetcode.com/uploads/2019/09/11/1359_ex1.png" style="width: 191px; height: 181px;" /></strong></p>

<pre>
<strong>Input:</strong> n = 8, m = 2, group = [-1,-1,1,0,0,1,0,-1], beforeItems = [[],[6],[5],[6],[3,6],[],[],[]]
<strong>Output:</strong> [6,3,4,1,5,2,0,7]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 8, m = 2, group = [-1,-1,1,0,0,1,0,-1], beforeItems = [[],[6],[5],[6],[3],[],[4],[]]
<strong>Output:</strong> []
<strong>Explanation:</strong>&nbsp;This is the same as example 1 except that 4 needs to be before 6 in the sorted list.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= m &lt;= n &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>group.length == beforeItems.length == n</code></li>
	<li><code>-1 &lt;= group[i] &lt;= m - 1</code></li>
	<li><code>0 &lt;= beforeItems[i].length &lt;= n - 1</code></li>
	<li><code>0 &lt;= beforeItems[i][j] &lt;= n - 1</code></li>
	<li><code>i != beforeItems[i][j]</code></li>
	<li><code>beforeItems[i]&nbsp;</code>does not contain&nbsp;duplicates elements.</li>
</ul>

class Solution {
public:
    vector<int> sortItems(int n, int m, vector<int>& group, vector<vector<int>>& beforeItems) {
        
        unordered_map<int, unordered_set<int>> groups;
        unordered_map<int, unordered_set<int>> graph;
        unordered_map<int, int> indegree;

        int ngsf = -1;
        for(int i = 0; i < n; i++)
        {
            if(indegree.find(i) == indegree.end())
                indegree[i] = 0;
            
            if(group[i] == -1){
                group[i] = ngsf;
                groups[ngsf--].insert(i);
            }
            else
                groups[group[i]].insert(i);
        }

        unordered_map<int, unordered_set<int>> order;
        unordered_map<int, int> ind_groups;


        for(int i = ngsf+1; i < m; i++)
        {
            for(auto j : groups[i])
                cout << j << " ";
            cout << endl;
            if(ind_groups.find(i) == ind_groups.end())
                ind_groups[i] = 0;
        }
        for(int i = 0; i < n; i++)
        {
            if(beforeItems[i].size() == 0)
                continue;
            for(auto before : beforeItems[i])
            {
                if(groups[group[i]].find(before) != groups[group[i]].end())
                {graph[before].insert(i);
                indegree[i]++;}
                else
                {
                    if(order[group[before]].find(group[i]) == order[group[before]].end())
{                    order[group[before]].insert(group[i]);
                    ind_groups[group[i]]++;}
                }
            }
        }

        //printing the graph
        // for(auto it : graph)
        // {
        //     cout << it.first << " :";

        //     for(auto k : it.second)
        //         cout << k << " ";
        //     cout << endl;
        // }

        // cout << "printing the order of groups to return" << endl;
        // for(auto it : order)
        // {
        //     cout << it.first << " :";

        //     for(auto k : it.second)
        //         cout << k << " ";
            
        //     cout << endl;
        // }
        //perform topo sort on each group
        unordered_map<int, vector<int>> topos;
        for(auto it : groups)
        {
            int group = it.first;
            auto nodes = it.second;

            cout << "group : " << group << endl;

            // cout << "nodes : " << endl;

            // for(auto z : nodes)
            //     cout << z << " ";
            // cout << endl;

            queue<int> q;

            for(auto node : nodes)
            {
                if(indegree[node] == 0)
                    q.push(node);
            }

            int vis = 0;
            vector<int> topo;
            while(not q.empty())
            {
                int node = q.front();
                q.pop();
                vis++;
                topo.push_back(node);

                if(graph.find(node) != graph.end())
                {
                    for(auto kid : graph[node])
                    {
                        indegree[kid]--;
                        if(not indegree[kid])
                            q.push(kid);
                    }
                }
            }
            // cout << " printing topo for each group : " << endl;
            // for(auto z : topo)
            //     cout << z << " ";

            // cout << endl;
            if(vis != nodes.size())
                return {};
            topos[group] = topo;
        }

        vector<int> final_order;
        queue<int> q;

        for(int i = ngsf+1; i < m; i++)
        {
            if(ind_groups[i] == 0)
                q.push(i), cout << i, cout << endl;
        }

        int vis = 0;

        while(not q.empty())
        {
            int node = q.front();
            q.pop();
            vis++;
            final_order.push_back(node);
            if(order.find(node) != order.end())
            {
                for(auto kid : order[node])
                {
                    ind_groups[kid]--;
                    if(not ind_groups[kid])
                        q.push(kid);
                }
            }
        }
        cout << "printing final order" << endl;
        for(auto z : final_order)
            cout << z << " ";
        cout << endl;
        if(vis != (m-ngsf-1))
            return {};
        
        vector<int> ans;
        for(auto i : final_order)
        {
            auto v = topos[i];
            for(auto j : v)
                ans.push_back(j);
        }
        return ans;
    }
};
114812