Return a valid task order

You are given `n` tasks labeled from `0` to `n - 1` and a list of prerequisite pairs `prerequisites`, where each pair `[a, b]` means task `b` must be completed before task `a`. Return any valid order in which all tasks can be completed. If it is impossible because the dependency graph contains a cycle, return an empty list. Example: - Input: `n = 4`, `prerequisites = [[1,0],[2,0],[3,1],[3,2]]` - Output: `[0,1,2,3]` or `[0,2,1,3]` Your solution should run efficiently for large inputs.