1203 - Sort Items by Groups Respecting Dependencies.

Hard

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:

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:

• <code>1 <= m <= n <= 3 * 10⁴</code>

• 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.