# 1203. Sort Items by Groups Respecting Dependencies

<https://leetcode.com/problems/sort-items-by-groups-respecting-dependencies>

## Description

There are `n` items each belonging to zero or one of `m` groups where `group[i]` is the group that the `i`-th item belongs to and it's equal to `-1` if the `i`-th item belongs to no group. The items and the groups are zero indexed. A group can have no item belonging to it.

Return a sorted list of the items such that:

* The items that belong to the same group are next to each other in the sorted list.
* There are some relations between these items where `beforeItems[i]` is a list containing all the items that should come before the `i`-th item in the sorted array (to the left of the `i`-th item).

Return any solution if there is more than one solution and return an **empty list** if there is no solution.

**Example 1:**

![](https://assets.leetcode.com/uploads/2019/09/11/1359_ex1.png)

```
**Input:** n = 8, m = 2, group = [-1,-1,1,0,0,1,0,-1], beforeItems = [[],[6],[5],[6],[3,6],[],[],[]]
**Output:** [6,3,4,1,5,2,0,7]
```

**Example 2:**

```
**Input:** n = 8, m = 2, group = [-1,-1,1,0,0,1,0,-1], beforeItems = [[],[6],[5],[6],[3],[],[4],[]]
**Output:** []
**Explanation:** This is the same as example 1 except that 4 needs to be before 6 in the sorted list.
```

**Constraints:**

* `1 <= m <= n <= 3 * 104`
* `group.length == beforeItems.length == n`
* `-1 <= group[i] <= m - 1`
* `0 <= beforeItems[i].length <= n - 1`
* `0 <= beforeItems[i][j] <= n - 1`
* `i != beforeItems[i][j]`
* `beforeItems[i]`does not contain duplicates elements.

## ac

```java
```