10.18 Interview Questions

Conceptual Questions

• What’s the difference between a list and a tuple?
• Why is list.append() O(1) amortized but list.insert(0, x) O(n)?
• What’s the difference between sort() and sorted()?
• What’s the difference between a shallow copy and a deep copy of a list?
• Why shouldn’t a mutable object be used as a function’s default argument value?

Scenario-Based Questions

• Every even number needs to be removed from a list while iterating — what’s the safe way to do it, and why does the naive approach fail?
• A function receives a list and appends to it — does the caller see the change? What if it received an int instead?
• A large list needs fast, repeated membership checks — what would change, and why?

Coding Questions

• Write a function to remove duplicates from a list while preserving order.
• Implement binary search on a sorted list without using any built-in search function.
• Given a list of dicts (like instance records), write a comprehension that extracts IDs matching a condition.

def remove_duplicates(l):
    return list(dict.fromkeys(l))

>>> remove_duplicates([3, 1, 3, 2, 1])
[3, 1, 2]

Quick Interview Answer

“List interview questions cluster around three things: confirming mutability and reference-sharing are understood (list vs. tuple, shallow vs. deep copy, the mutable-default-argument trap), knowing the time complexity trade-offs that drive real design decisions (append vs. insert(0, ...), list membership vs. a set), and classic coding problems — safe removal during iteration, order-preserving deduplication, binary search — that test comfort with slicing, dict.fromkeys(), and index arithmetic rather than memorized syntax.”

Common Mistakes

• Answering “a list and a tuple are basically the same, just different brackets” without mentioning mutability, hashability, or the performance/memory implications.
• Solving the “remove while iterating” scenario by suggesting a while loop with manual index tracking instead of the simpler iterate-over-a-copy pattern.
• Forgetting binary search’s precondition — the list must already be sorted — and describing it as a general-purpose search technique.