Stack Trace And Profiler Log Processing

What's being tested

This tests stack simulation over ordered execution logs: reconstruct active calls, compute inclusive and exclusive time, and emit derived trace events. Interviewers are probing careful interval reasoning, edge-case handling, and clean O(n) stream-processing code.

Patterns & templates

• Call-stack simulation — maintain stack[(fn, start_ts, child_time)]; on end, exclusive time is end - start - child_time.

• Previous-timestamp accounting — for LeetCode-style start/end logs, charge ts - prev_ts to stack[-1]; update prev_ts after each event.

• Stack sample diffing — compare old and new frame arrays by longest common prefix; emit end events deepest-first, start events shallowest-first.

• Call tree reconstruction — parse indentation, frame depth, or parent IDs; attach nodes via a stack of current ancestors in O(n) time.

• Streaming validation — detect missing end, impossible end order, negative durations, equal timestamp ambiguity, and recursion by tracking frame identity.

• Complexity target — aim for O(n) time and O(d) space, where d is max stack depth; aggregate per-function maps separately.

Common pitfalls

Pitfall: Confusing inclusive time with exclusive time; parent time must subtract completed child intervals or only receive gaps while active.

Pitfall: Handling equal timestamps inconsistently; declare whether intervals are half-open [start, end) or inclusive, then apply it everywhere.

Pitfall: Treating function name as unique identity during recursion; recursive calls need separate stack frames even when fn is identical.

Practice these

The practice cards below cover the canonical variants — solve all of them and time yourself.