How should I practice Topological Ordering?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Apple onsite interview problems in FastPrep.

Is Topological Ordering associated with Apple?

FastPrep tags this as a Apple onsite interview coding practice problem when the problem catalog has that company and stage context.

Topological Ordering

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Problem statement

There are n vertices numbered from 0 through n - 1. Each directed edge [u, v] requires u to appear before v.

Return the lexicographically smallest ordering containing every vertex exactly once and satisfying every edge. If no such ordering exists because the graph contains a directed cycle, return an empty array. With zero vertices, the result is also an empty array.

Function

topologicalOrder(n: int, edges: int[][]) → int[]

Examples

Example 1

n = 4edges = [[0,2],[1,2]]return = [0,1,2,3]

Choose the smallest currently available vertex; isolated vertex 3 still appears.

Example 2

n = 3edges = [[0,1],[1,2],[2,0]]return = []

The cycle prevents any ordering of all vertices.

Example 3

n = 3edges = [[2,0]]return = [1,2,0]

Vertex 0 must wait for vertex 2; vertex 1 is the smallest available first choice.

Constraints

0 <= n <= 2000.
There are at most 2000 edges.
Every edge endpoint is in [0, n).
Repeated edges and self-loops are allowed.