Is the schedule order unique?

Given jobs and their dependencies (("curves", "swaps") means curves before swaps), decide whether there is exactly one valid execution order. If two or more valid orders exist, or if the dependencies are cyclic (no order at all), return False.

jobs = ["a", "b", "c"]
deps = [("a", "b"), ("b", "c")]      ->   True    (only a, b, c works)

jobs = ["a", "b", "c"]
deps = [("a", "b"), ("a", "c")]      ->   False   (a, b, c and a, c, b both work)

Return whether the topological order is unique. Aim for $O(V + E)$.