Sort Items by Groups Respecting Dependencies
<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://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1200-1299/1203.Sort%20Items%20by%20Groups%20Respecting%20Dependencies/images/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>
Depth-First Search; Breadth-First Search; Graph; Topological Sort
function sortItems(n: number, m: number, group: number[], beforeItems: number[][]): number[] {
    let idx = m;
    const groupItems: number[][] = new Array(n + m).fill(0).map(() => []);
    const itemDegree: number[] = new Array(n).fill(0);
    const gorupDegree: number[] = new Array(n + m).fill(0);
    const itemGraph: number[][] = new Array(n).fill(0).map(() => []);
    const groupGraph: number[][] = new Array(n + m).fill(0).map(() => []);
    for (let i = 0; i < n; ++i) {
        if (group[i] === -1) {
            group[i] = idx++;
        }
        groupItems[group[i]].push(i);
    }
    for (let i = 0; i < n; ++i) {
        for (const j of beforeItems[i]) {
            if (group[i] === group[j]) {
                ++itemDegree[i];
                itemGraph[j].push(i);
            } else {
                ++gorupDegree[group[i]];
                groupGraph[group[j]].push(group[i]);
            }
        }
    }
    let items = new Array(n + m).fill(0).map((_, i) => i);
    const topoSort = (graph: number[][], degree: number[], items: number[]): number[] => {
        const q: number[] = [];
        for (const i of items) {
            if (degree[i] === 0) {
                q.push(i);
            }
        }
        const ans: number[] = [];
        while (q.length) {
            const i = q.pop()!;
            ans.push(i);
            for (const j of graph[i]) {
                if (--degree[j] === 0) {
                    q.push(j);
                }
            }
        }
        return ans.length === items.length ? ans : [];
    };
    const groupOrder = topoSort(groupGraph, gorupDegree, items);
    if (groupOrder.length === 0) {
        return [];
    }
    const ans: number[] = [];
    for (const gi of groupOrder) {
        items = groupItems[gi];
        const itemOrder = topoSort(itemGraph, itemDegree, items);
        if (itemOrder.length !== items.length) {
            return [];
        }
        ans.push(...itemOrder);
    }
    return ans;
}
