<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:
    void fun(int g,vector<int>& grp,vector<int>& inDeg,vector<vector<int>>& adj,vector<int>& topoSort,vector<int>& vec){
        queue<int> q;
        int n=grp.size();
        for(int i: vec){
            // cout<<i<<" ";
            if(inDeg[i]==0){
                q.push(i);
            }
        }
        while(q.size()){
            int i=q.front();
            topoSort.push_back(i);
            q.pop();
            for(auto& j: adj[i]){
                if(--inDeg[j]==0 && grp[j]==g) q.push(j);
            }
        }
        // cout<<endl;
    }
    vector<int> grpGrphSort(int n,vector<int>& inDeg,vector<unordered_set<int>>& adjGrpGrph){
        vector<int> topoSort;
        queue<int> q;
        for(int i=0;i<n;i++){
            if(inDeg[i]==0){
                q.push(i);
            }
        }
        while(q.size()){
            int i=q.front();
            topoSort.push_back(i);
            q.pop();
            for(auto& j: adjGrpGrph[i]){
                if(--inDeg[j]==0) q.push(j);
            }
        }
        return topoSort;
    }
    vector<int> sortItems(int n, int m, vector<int>& grp, vector<vector<int>>& befItm) {
        vector<vector<int>> adj(n);
        vector<vector<int>> newGrp(n);
        for(int i=0;i<n;i++){
            for(int& j: befItm[i]){
                adj[j].push_back(i);
            }
        }
        int firstNonGrpEle=-1;
        int firstEmptyGrp=0;
        for(int i=0;i<n;i++){
            if(grp[i]!=-1){
                newGrp[grp[i]].push_back(i);
                while(firstEmptyGrp<n && newGrp[firstEmptyGrp].size()) firstEmptyGrp++;
            }
            else if(firstNonGrpEle==-1) firstNonGrpEle=i;
        }

        if(firstNonGrpEle!=-1){
            while(firstNonGrpEle<n){
                grp[firstNonGrpEle]=firstEmptyGrp;
                newGrp[firstEmptyGrp].push_back(firstNonGrpEle);
                while(firstNonGrpEle<n && grp[firstNonGrpEle]!=-1) firstNonGrpEle++;
                while(firstEmptyGrp<n && newGrp[firstEmptyGrp].size()) firstEmptyGrp++;
            }
        }
        // for(int i=0;i<n;i++){
        //     for(int j: newGrp[i]) cout<<j<<" ";
        //     cout<<endl;
        // }
        vector<unordered_set<int>> adjGrpGrph(n);
        for(int i=0;i<n;i++){
            for(int& j: adj[i]){
                if(grp[i]!=grp[j]) adjGrpGrph[grp[i]].insert(grp[j]);
            }
        }
        vector<int> inDeg(n,0);
        for(int i=0;i<n;i++){
            for(auto& j: adjGrpGrph[i]){
                inDeg[j]++;
            }
        }
        vector<int> ans=grpGrphSort(n,inDeg,adjGrpGrph);
        if(ans.size()<n) return {};
        vector<int> topoSort;
        for(int i=0;i<n;i++){
            for(auto& j: adj[i]){
                inDeg[j]++;
            }
        }
        for(int i=0;i<n;i++) fun(ans[i],grp,inDeg,adj,topoSort,newGrp[ans[i]]);
        if(topoSort.size()<n) return {};
        return topoSort;
    }
};
99512