LeetCode 1203 Sort Items by Groups Respecting Dependencies - Problem Statement

Given n items belonging to m groups, and dependencies between items, sort items so that:

1. All dependencies are satisfied (if item a depends on b, b comes before a).
2. Items in the same group are adjacent.

Items with group -1 can go anywhere (treat each as its own group).

With n=8, m=2, group=[-1,-1,1,0,0,1,0,-1], beforeItems=[[],[6],[5],[6],[3,6],[],[],[]:

• Item 2 depends on 5, item 3 depends on 6, item 4 depends on 3 and 6.
• Valid order: [6,3,4,1,5,2,0,7] or similar.

Return empty array if impossible.

Constraints: $1 \le n \le 30000$. $1 \le m \le n$.