<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) {
        vector<int> nodeIndegree(n);
        vector<int> adj[n];
        unordered_map<int, int> groupIndegree;
        unordered_map<int, unordered_set<int>> groupAdj;
        unordered_map<int, vector<int>> groupToNode;
        for(int i = 0; i < group.size(); ++i) {
            if(group[i] == -1)
                group[i] = m++;
            groupToNode[group[i]].push_back(i);
            groupIndegree[group[i]] = 0;
        }
        for(int i = 0; i < beforeItems.size(); ++i) {
            int currentGroup = group[i];
            for(int j = 0; j < beforeItems[i].size(); ++j) {
                int dependentGroup = group[beforeItems[i][j]];
                if(currentGroup != dependentGroup && groupAdj[dependentGroup].count(currentGroup) == 0) {
                    groupAdj[dependentGroup].insert(currentGroup);
                    groupIndegree[currentGroup]++;
                }
                adj[beforeItems[i][j]].push_back(i);
                nodeIndegree[i]++;
            }
        }
        queue<int> groupQueue;
        for(auto x: groupIndegree) {
            cout << x.first << " " << x.second << endl;
            if(x.second == 0) {
                // cout << x.first << endl;
                groupQueue.push(x.first);
            }
        }
        vector<int> ans;
        while(!groupQueue.empty()) {
            int currentGroup = groupQueue.front(); groupQueue.pop();
            cout << "currentGroup => " << currentGroup << endl;
            for(int childGroup: groupAdj[currentGroup]) {
                groupIndegree[childGroup] -= 1;
                if(groupIndegree[childGroup] == 0) {
                    groupQueue.push(childGroup);
                }
            }
            queue<int> nodeQueue;
            vector<int> nodes = groupToNode[currentGroup];
            for(int i = 0; i < nodes.size(); ++i) {
                if(nodeIndegree[nodes[i]] == 0) {
                    nodeQueue.push(nodes[i]);
                }
            }
            while(!nodeQueue.empty()) {
                int node = nodeQueue.front(); nodeQueue.pop();
                cout << "node => " << node << endl;
                ans.push_back(node);
                for(int childNode: adj[node]) {
                    cout << "childNode => " << childNode << endl;
                    nodeIndegree[childNode] -= 1;
                    if(nodeIndegree[childNode] == 0 && group[childNode] == currentGroup) {
                        cout << "i am on dependency zero => " << childNode << endl;
                        nodeQueue.push(childNode);
                    }
                    // cout << "childNode => " << childNode << endl;
                }   
            }
        }
        for(int i = 0; i < nodeIndegree.size(); ++i) {
            if(nodeIndegree[i] != 0)
                return {};
        }
        return ans;
    }
};
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