This is the follow-up to the basic call-stack parser, so you're expected to already have the core structure in your head.
Clarify the input format (e.g., list of strings like 'enter f' and 'exit f') and define depth as the number of active calls. Then iterate through the trace, incrementing a counter on enter and decrementing on exit, tracking the maximum value seen. This yields an O(n) time, O(1) space solution.
Pro tip: Mention that you can validate the trace by checking that depth never goes negative and ends at zero, which shows you think about robustness and edge cases.
Ask about the trace format (e.g., list of strings, events with function names) and confirm that depth is the number of currently active function calls. Ensure you know what to return (maximum depth).
Initialize a current depth counter to 0 and a max depth variable to 0. Explain that each 'enter' increases depth by 1 and each 'exit' decreases it by 1.
Loop through each event in order. On 'enter', increment current depth and update max if current > max. On 'exit', decrement current depth.
Consider empty trace (return 0), unbalanced traces (depth goes negative or doesn't end at 0), and nested calls. Mention that you can optionally validate the trace.
State that the algorithm runs in O(n) time and O(1) extra space, where n is the number of events. This is optimal since you must read each event at least once.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Use a hash map to maintain a separate stack depth counter for each thread ID, updating on enter and exit events. Track the maximum depth per thread as you process events, then return the maximums. This approach is O(n) time and O(t) space, where t is the number of threads.
Pro tip: Mention that you assume the event trace is well-formed (no unmatched exits) and discuss how you would handle invalid traces, such as ignoring exits when the stack is empty or logging errors. This shows attention to edge cases and production readiness.
Confirm that each event has a thread ID and type (enter/exit), and that the trace is per-thread consistent. Ask about handling malformed traces (e.g., exit without enter) and whether thread IDs are bounded.
Use a hash map (dictionary) to map thread ID to its current stack depth, and another hash map to store the maximum depth seen per thread. This allows O(1) updates per event.
Iterate through the event trace. For each event, update the current depth for that thread: increment on enter, decrement on exit. After each update, compare and update the maximum depth for that thread.
If an exit event would make depth negative, either ignore it or raise an error based on requirements. Document this behavior.
After processing all events, return a mapping from thread ID to its maximum stack depth. If a thread never appeared, it may be omitted or included with depth 0, depending on requirements.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.