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.