**Preserve Order:** dict.fromkeys(s) (Py 3.7+ insertion order) or seen=set(); ''.join(c for c in s if c not in seen and not seen.add(c)). **Complexity:** O(n). set/dict for O(1) lookup. For large strings: generator avoids full materialization....
This medium-level Python/Coding question appears frequently in data engineering interviews at companies like EY. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (join, python) will help you answer variations of this question confidently.
Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.
Preserve Order: dict.fromkeys(s) (Py 3.7+ insertion order) or seen=set(); ''.join(c for c in s if c not in seen and not seen.add(c)).
Complexity: O(n). set/dict for O(1) lookup. For large strings: generator avoids full materialization.
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Analyze My Answer — FreeAccording to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.