Code Room
CodingMedium
Question
Return the number of prime numbers strictly less than a given non-negative integer n. For example, there are 4 primes below 10 (2, 3, 5, 7). n can be up to 5,000,000. Aim for a solution that runs well within a few seconds at the upper bound.
Implement
count_primes(n: int) → intExamples
in
[10]out4What 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.