<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) {
        for(int i=0;i<group.size();i++){
            if(group[i]==-1)group[i]=m++;
        }
        map<int,vector<int>> mp;
        for(int i=0;i<group.size();i++)group[i]++;
        vector<int> adj[n+1];
        vector<int> adj1[m+1];
        vector<int> ind(n+1,0),in(m+1,0);

        map<pair<int,int>,int> grpedge;
        for(int i=0;i<beforeItems.size();i++){
            if(beforeItems[i].empty())continue;
            for(auto it:beforeItems[i]){
                adj[it].push_back(i);
                ind[i]++;
               
                if(group[i]!=group[it]){
                    if(grpedge.find({group[it],group[i]})!=grpedge.end())continue;
                    adj1[group[it]].push_back(group[i]);
                    in[group[i]]++;
                    grpedge[{group[it],group[i]}]++;
                }
            }
        }
        for(int i=0;i<group.size();i++){
            mp[group[i]].push_back(i);
        }
        int val=0;
        queue<int> q;
        map<int,int> item,grp;
        for(int i=0;i<n;i++){
            if(ind[i]==0)q.push(i);
        }
        while(!q.empty()){
            int sz=q.size();
            for(int i=0;i<sz;i++){
                auto tp=q.front();
                item[tp]=val++;
                q.pop();
                for(auto it:adj[tp]){
                    if(--ind[it]!=0)continue;
                    q.push(it);
                }
            }
        }
        if(val!=n)return {};
        val=0;
        for(int i=0;i<=m;i++){
            if(in[i]==0)q.push(i);
        }
        while(!q.empty()){
            int sz=q.size();
            for(int i=0;i<sz;i++){
                auto tp=q.front();
                grp[tp]=val++;
                q.pop();
                for(auto it:adj1[tp]){
                    if(--in[it]!=0)continue;
                    q.push(it);
                }
            }
        }
        // cout<<val<<" "<<m;
        if(val!=(m+1))return {};
        vector<pair<int,int>> x;
        for(auto it:grp){
            x.push_back({it.second,it.first});
        }
        vector<int> ans;
        sort(x.begin(),x.end());
        for(auto it:x){
            vector<pair<int,int>> y;
            for(auto ti:mp[it.second]){
                y.push_back({item[ti],ti});
            }
            sort(y.begin(),y.end());
            for(auto ti:y)
                ans.push_back(ti.second);
        }
        if(ans.size()!=n)return {};
        return ans;

    }
};
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