<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> topo_sort(vector<vector<int>>& adj ){
        // int count=0;
        // for(auto j:adj){
        //     cout<<count++<<" -> ";
        //     for( auto i:j){
        //         cout<<i<<" ";
        //     }
        //     cout<<endl;
        // }
        // indegree;
        int n= adj.size();
        vector<int> indegree( n,0 );
        for(auto ad:adj){
            for( auto i:ad){
                indegree[i]++;
            }
        }
        vector<bool> visited(n,0);
        queue<int> qu;
        for( int i=0;i<n;i++){
            if(indegree[i]==0){
                indegree[i]--;
                visited[i]=1;
                qu.push(i);
            }
        }
        vector<int> ret;
        while(!qu.empty()){
            int tp = qu.front();
            qu.pop();
            ret.push_back(tp);
            for(auto j: adj[tp]){
                indegree[j]--;
                if(indegree[j]==0 && visited[j]==0){
                    visited[j]=1;
                    qu.push(j);
                }
            }
        }

        if(ret.size() != n) return {};
        return ret;
    }
    vector<int> sortItems(int n, int m, vector<int>& group, vector<vector<int>>& beforeItems) {
        vector<vector<int>> graph_item(n);
        for(int i=0;i<n;i++){
            // create new group for -1
            if(group[i]==-1){
                group[i]=m++;
            }
            // create item to item adj list
            if(beforeItems[i].size()!= 0){
                for(auto j: beforeItems[i] ){
                    graph_item[j].push_back(i);
                }
            }
        }

        vector<vector<int>> graph_grp(m);
        for(int i=0;i<n;i++){
            // create grp to grp adj list
            int self_grp = group[i];
            if(beforeItems[i].size()!= 0){
                for(auto j: beforeItems[i] ){
                    int grp_bef = group[j];
                    if( grp_bef != self_grp){
                        graph_grp[grp_bef].push_back(self_grp);
                    }
                }
            }
        }
        vector<int> topo_item = topo_sort(graph_item);
        if(topo_item.size()==0) return {};
        // for(auto i: topo_item){
        //     cout<<i<<" ";
        // }
        // cout<<endl;
        vector<int> topo_grp = topo_sort(graph_grp);
        if(topo_grp.size()==0) return {};
        // for(auto i: topo_grp){
        //     cout<<i<<" ";
        // }
        // cout<<endl;
        vector<vector<int>> ans(m);
        for(auto i: topo_item){
            ans[group[i]].push_back(i);
        }
        vector<int> ret;
        for(int i:topo_grp){
            for(auto j: ans[i]){
                ret.push_back(j);
            }
        }

        return ret;

        

    }
};
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