Model the tasks and dependencies as a directed graph and perform a topological sort using Kahn's algorithm (BFS with in-degree tracking) or DFS with cycle detection. If the topological order contains all tasks, return it; otherwise, report that no valid schedule exists due to a cycle.
Pro tip: Explicitly discuss how you would handle large-scale dependency graphs, such as using iterative DFS to avoid stack overflow or parallelizing the topological sort for distributed systems, showing awareness of Netflix's scale.
Confirm the input format (e.g., adjacency list or edge list), whether tasks are uniquely identified, and if multiple valid orders are acceptable. Ask about constraints like graph size or performance requirements.
Select topological sort via Kahn's algorithm (BFS) or DFS with cycle detection. Explain why it fits: O(V+E) time, handles cycles, and produces a valid order.
Describe the steps: compute in-degrees, initialize a queue with zero in-degree nodes, process nodes while decrementing in-degrees of neighbors, and enqueue when in-degree becomes zero. For DFS, use recursion with temporary marks to detect cycles.
If the result list size is less than the number of tasks, a cycle exists; return an error or empty list. Discuss edge cases: empty graph, disconnected components, self-loops, and duplicate edges.
State time and space complexity: O(V+E) time, O(V) space. Suggest testing with acyclic graphs, cyclic graphs, and large graphs to ensure correctness and performance.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying requirements and defining the Command interface with execute and undo methods. Then design a CommandInvoker that maintains a stack of executed commands, handling edge cases like empty stack by throwing a custom exception or no-op. Discuss trade-offs such as memory usage, thread safety, and whether to support redo.
Pro tip: Mention that you would use a stack to track commands and consider using the Memento pattern to capture state for undo, but be mindful of memory overhead for large states. Also, proactively discuss how to handle exceptions during execute to avoid corrupting the undo stack.
Ask about expected command types, whether redo is needed, thread safety, and persistence requirements. This shows you think about the broader context before diving into code.
Design an interface with execute() and undo() methods. Each concrete command encapsulates the action and the state needed to reverse it, following the Command pattern.
Create an invoker that holds a stack of executed commands. On execute, run the command and push it onto the stack. On undo, pop the most recent command and call its undo method.
For undo when stack is empty, throw a custom exception like NoCommandToUndoException or return a boolean indicating failure. Also consider what happens if execute fails midway—ensure the command is not pushed or is rolled back.
Talk about memory vs. performance (storing full state vs. deltas), thread safety (synchronized stack or concurrent data structure), and optional redo support using a second stack.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.