Code Room
CodingMedium
Question
Given an array a of length n where every value is in the range [1, n], some values appear once and some appear exactly twice. Return a sorted list of all values that appear twice. Aim for O(n) time and O(1) extra space (not counting the output).
Implement
find_duplicates(a: list[int]) → list[int]Examples
in
[[4,3,2,7,8,2,3,1]]out[2,3]What a strong answer looks like
State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Learn the concepts
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.
Run or narrate your approach, then ask the coach.