<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> getItemsTopo(map<int, vector<int>>& adjList, map<int, set<int>>& groupMap, int groupNum) {
        map<int, int> indegreeMap;
        for(auto node : groupMap[groupNum]) {
            indegreeMap[node] = 0;
        }

        for(auto node : groupMap[groupNum]) {
            for(auto adjNode : adjList[node]) {
                if(indegreeMap.count(adjNode)) {
                    indegreeMap[adjNode]++;
                }
            }
        }

        queue<int> q;
        for(auto [node, indegree] : indegreeMap) {
            if(indegree == 0) {
                q.push(node);
            }
        }

        if(q.empty()) return {};
        vector<int> topo;

        while(!q.empty()) {
            auto curnode = q.front();
            topo.push_back(curnode);
            q.pop();

            for(auto adjNode : adjList[curnode]) {
                if(indegreeMap.count(adjNode)) {
                    indegreeMap[adjNode]--;
                    if(indegreeMap[adjNode] == 0) {
                        q.push(adjNode);
                    }
                }
            }
        }
        vector<int> empty;
        return topo.size() != indegreeMap.size() ? empty : topo;
    }

    vector<int> getGroupsTopo(map<int, vector<int>>& adjList) {
        vector<int> topoSort;
        unordered_map<int,int> indegreeMap;
        for(auto& [node, adjNodes] : adjList) {
            if(indegreeMap.count(node) == 0) indegreeMap[node] = 0;
            for(auto adjNode : adjNodes) {
                indegreeMap[adjNode]++;
            }
        }

        queue<int> q;

        for(auto& [node, indegree] : indegreeMap) {
            if(indegree == 0) q.push(node);
        }

        if(q.empty()) return topoSort;

        while(!q.empty()) {
            auto curNode = q.front();
            topoSort.push_back(curNode);
            q.pop();

            for(auto adjNode : adjList[curNode]) {
                indegreeMap[adjNode]--;
                if(indegreeMap[adjNode] == 0) {
                    q.push(adjNode);
                }
            }
        }
        vector<int> empty;
        return topoSort.size() == indegreeMap.size() ? topoSort : empty;
    }

    vector<int> sortItems(int n, int m, vector<int>& group, vector<vector<int>>& beforeItems) {
        int maxGroup = *max_element(group.begin(), group.end());
        int extraGroup = maxGroup+1;

        map<int, vector<int>> itemsAdjList;
        for(int i = 0; i<n; i++) {
            for(auto node : beforeItems[i]) {
                itemsAdjList[node].push_back(i);
            }
        }

        if(itemsAdjList.size() == 0) {
            vector<int> ans;
            for(int g = -1; g < m; g++) {
                for(int i = 0; i<n; i++) {
                    if(group[i] == g) {
                        ans.push_back(i);
                    }
                }
            }
            return ans;
        }

        map<int, set<int>> groupMap;

        map<int, vector<int>> groupAdjList;
        for(auto& pr : itemsAdjList) {
            auto& [node, adjNodes] = pr;
            int nodeGroup = group[node];
            if(nodeGroup == -1) {
                nodeGroup = extraGroup++;
                group[node] = nodeGroup;
            }

            groupMap[nodeGroup].insert(node);
            if(groupAdjList.count(nodeGroup) == 0) groupAdjList[nodeGroup] = {};

            for(auto adjNode : adjNodes) {
                if(group[adjNode] != nodeGroup) {
                    if(group[adjNode] == -1) {
                        groupAdjList[nodeGroup].push_back(extraGroup);
                        groupMap[extraGroup].insert(adjNode);
                        group[adjNode] = extraGroup;
                        extraGroup++;
                    }
                    else {
                        groupAdjList[nodeGroup].push_back(group[adjNode]);
                        groupMap[group[adjNode]].insert(adjNode);
                    }
                }
            }
        }
        for(int i = 0; i<n; i++) {
            groupMap[group[i]].insert(i);
        }

        vector<int> groupTopo = getGroupsTopo(groupAdjList);
        if(groupTopo.size() == 0) return {};

        vector<int> ans;
        for(auto groupNumber : groupTopo) {
            vector<int> subAns = getItemsTopo(itemsAdjList, groupMap, groupNumber);
            if(subAns.size() == 0) return {};
            for(auto item : subAns)
                ans.push_back(item);
        }

        for(int i = 0; i<n; i++) {
            if(group[i] == -1) {
                ans.push_back(i);
            }
        }

        for(int g = 0; g<m; g++) {
            if(groupAdjList.count(g) == 0) {
                for(auto node : groupMap[g]) {
                    ans.push_back(node);
                }
            }
        }

        return ans;
    }
};
94412