<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:
    static bool cmp(vector<int>&a,vector<int>&b)
    {
        if(a[0]!=b[0])return a[0]<b[0];
        else return a[1]<b[1];
    }
    vector<int> sortItems(int n, int m, vector<int>& group, vector<vector<int>>& beforeItems) {
        vector<int>graph[n];
        vector<int>ind(n);
        int groupId = m;
        for(int i=0;i<n;i++)
        {
            if(group[i]==-1)group[i] = groupId++;
        }
        for(int i=0;i<n;i++)
        {
            for(auto val:beforeItems[i])
            {
                graph[val].push_back(i);
                ind[i]++;
            }
            
        }
        queue<int>q;
        for(int i=0;i<n;i++)if(ind[i]==0)q.push(i);
        vector<int>elements;
        while(!q.empty())
        {
            auto f=q.front();
            q.pop();
            elements.push_back(f);
            for(auto val:graph[f])
            {
                ind[val]--;
                if(ind[val]==0)q.push(val);
            }
        }
        if(elements.size()<n)return {};


        map<int,vector<int>>groups;
        vector<int>in(groupId);
        set<pair<int,int>>st;
        for(int i=0;i<n;i++)
        {
            int x=group[i];
            for(auto val:beforeItems[i])
            {
                if(st.find({group[val],x})==st.end() && x!=group[val])
                {groups[group[val]].push_back(x);
                in[x]++;
                st.insert({group[val],x});
                }
            }
            
        }
        queue<int>pq;
        for(int i=0;i<groupId;i++)if(in[i]==0)pq.push(i);
        vector<int>grp;
        while(!pq.empty())
        {
            auto f=pq.front();
            pq.pop();
            grp.push_back(f);
            for(auto val:groups[f])
            {
                in[val]--;
                if(in[val]==0)
                {
                    pq.push(val);
                }
            }
        }
        if(grp.size()<groupId)return {};
        unordered_map<int,int>index;
        for(int i=0;i<grp.size();i++)
        {
            index[grp[i]]=i;
        }
        vector<vector<int>>ans;
        for(int i=0;i<elements.size();i++)
        {
             vector<int>temp;
             temp.push_back(index[group[elements[i]]]);
             temp.push_back(i);
             temp.push_back(elements[i]);
             ans.push_back(temp);
        }
        sort(ans.begin(),ans.end(),cmp);
        vector<int>sol;
        for(auto val:ans)
        {
            sol.push_back(val[2]);
        }
        return sol;
    }
};
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