Sensor Network III
Field sensors numbered 0 to n − 1 are linked by directed edges (u, v): data flows from u to v, so u must be processed before v. Return an order in which all the sensors can be processed, or an empty list when a cycle makes that impossible. Any valid order is accepted.
n = 4, edges = [[0, 1], [0, 2], [1, 3], [2, 3]] -> [0, 1, 2, 3] (or [0, 2, 1, 3]) n = 2, edges = [[0, 1], [1, 0]] -> []
Hints
Hint 1
Count each sensor's incoming edges. A sensor with none can be processed now; processing it removes its outgoing edges.
Hint 2
If you run out of sensors with no remaining inputs before placing all n, the rest sit on or behind a cycle.