Fizz Buzz

Loop i from one through n and build the required output for each value. Check divisibility by both three and five before checking either one alone, because multiples of fifteen must produce the combined label rather than just the first branch. Otherwise emit the three label, the five label, or the number itself. State whether the API returns strings, prints lines, or builds an array, since that affects testability and output cost. Test n zero if allowed, n one, three, five, fifteen, and a value just beyond fifteen. The divisibility checks are constant time, so the algorithm is O(n) time and O(n) output space if an array of n strings is returned; printing directly uses O(1) auxiliary space. Avoid overengineering this into maps or recursion, but mention that rule ordering is the actual correctness risk.