Use OrderedDict to dedupe stably

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Q: What difficulty level is this coding question?

This is a Medium difficulty Data Manipulation (SQL/Python) question, commonly asked during Technical Screen rounds at Yahoo.

Q: What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Yahoo during technical interviews.

Question

Implement dedupe_preserve_order(seq) that removes duplicates from a list while preserving the order of first appearance, in O(n) time and O(k) space (k = number of unique items). Use collections.OrderedDict (or dict in Python 3.7+) and do not use nested loops or list.index. The function must treat strings case-insensitively for deduplication but return the original casing of the first occurrence. For example, input ['A','b','a','B','c','C','b'] should return ['A','b','c']. Explain the time/space complexity and how your solution behaves if elements are not hashable.

PracHub · Accepted Answer

This question evaluates a candidate's ability to implement stable deduplication using Python's ordered mapping types while handling case-insensitive comparisons that preserve original casing, and to reason about algorithmic complexity such as O(n) time and O(k) space.

Quick Overview

Use OrderedDict to dedupe stably