Netflix·Software Engineer·Technical Phone Screen·Senior

Senior

May 2026

Summary

Netflix coding round focused on graph algorithms. The topological sort question covered both major approaches and you had to know your cycle detection too, not just the happy path.

Questions Asked (1)

Given a directed graph with n nodes and a list of directed edges, return any valid topological ordering of the nodes. If the graph contains a cycle, report that no valid ordering exists.

Algorithms & Data Structures

Author's notes

Two approaches came up: the BFS-based in-degree method and the DFS with coloring.

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AI HintsAI Generated

Suggested Approach

Use Kahn's algorithm (BFS-based) to compute in-degrees, repeatedly remove nodes with zero in-degree, and build the topological order. If the order doesn't include all nodes, a cycle exists. Alternatively, use DFS with cycle detection via recursion stack.

Pro tip: Mention that Kahn's algorithm naturally detects cycles by checking if the result size equals n, and it's iterative, avoiding recursion depth issues. Also, note that topological order is not unique, so any valid order is acceptable.

1. Clarify graph representation and constraints

Confirm if the graph is given as adjacency list or edge list, and discuss constraints like n and edge count to choose the right algorithm.

2. Choose algorithm and explain approach

Decide between Kahn's algorithm (BFS) or DFS. Explain the steps: compute in-degrees, use a queue for zero in-degree nodes, and process.

3. Implement topological sort with cycle detection

Write code to perform the chosen algorithm, ensuring cycle detection by checking if all nodes are processed.

4. Analyze complexity and edge cases

State time and space complexity (O(V+E) time, O(V) space) and discuss edge cases like empty graph, single node, or disconnected components.

5. Test with examples

Walk through a simple example (e.g., DAG and cyclic graph) to verify correctness and demonstrate understanding.

Key Points to Mention

Topological sort is only possible for Directed Acyclic Graphs (DAGs).
Kahn's algorithm uses in-degree and a queue; DFS uses recursion stack for cycle detection.
Cycle detection: if the topological order doesn't include all nodes, a cycle exists.
Time complexity: O(V+E) for both algorithms; space complexity: O(V) for storing in-degrees and queue/stack.
Multiple valid topological orders may exist; any is acceptable.
Handling disconnected graphs: ensure all nodes are considered, e.g., by initializing queue with all zero in-degree nodes.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.