My first instinct was to just track a boolean flag for whether we're 'inside' a session.
Clarify the log format and what constitutes a valid sequence, then use a stack to track open events and ensure each end matches the most recent start. Walk through the list, pushing starts and popping on ends, returning false if an end appears without a matching start or if the stack isn't empty at the end.
Pro tip: Before coding, discuss edge cases like empty input, nested events, and interleaved logs; this shows you think about robustness and real-world scenarios, which interviewers at Meta value.
Ask questions to understand the log format, what defines a valid sequence, and whether nesting is allowed. Confirm assumptions about input size and constraints.
Recognize that a stack is ideal for tracking open events because it enforces last-in-first-out matching. Explain why other structures like queues or sets are less suitable.
Describe iterating through the logs: push on start, pop on end, and validate that the popped start matches the end. Return false immediately if an end has no matching start.
Consider empty input, logs with only starts or only ends, and nested or interleaved sequences. Ensure the algorithm returns false for any invalid case.
State that time complexity is O(n) and space is O(n) in the worst case. Walk through a few examples to verify correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.