Find a valid dependency order

You are given n tasks labeled from 0 to n - 1 and a list of dependency pairs dependencies, where each pair [a, b] means task b must be completed before task a.

Return any valid ordering of all tasks that satisfies the dependencies. If no such ordering exists because the dependency graph contains a cycle, return an empty list.

Example:

• Input: n = 4, dependencies = [[1,0],[2,0],[3,1],[3,2]]
• Valid output: [0,1,2,3] or [0,2,1,3]

Discuss the time and space complexity of your approach.