L1 · FoundationsNumbers & loops~3 min · 4 tests

FizzBuzz in Python

Solve FizzBuzz in Python: return 1..n with multiples of 3 as Fizz, 5 as Buzz and both as FizzBuzz. The classic first interview question, run live.

The problem

Return a list of strings for the numbers 1..n:

multiples of both 3 and 5 → "FizzBuzz"
multiples of 3 → "Fizz"
multiples of 5 → "Buzz"
anything else → the number as a string

Examples

Example 1

Input

fizzbuzz(5)

Expected output

['1', '2', 'Fizz', '4', 'Buzz']

Example 2

Input

fizzbuzz(15)

Expected output

['1', '2', 'Fizz', '4', 'Buzz', 'Fizz', '7', '8', 'Fizz', 'Buzz', '11', 'Fizz', '13', '14', 'FizzBuzz']

+ 2 hidden tests on Submit.

Edge cases to ask about

n = 0
n = 1

Hints

0/3

How an interviewer scores this

0/9

1. Understand the problemRestate it, ask about edge cases and input size.
2. Write a brute-force solutionCorrect first, clever later.
3. Get the correct outputautoAll visible examples pass.
4. Analyse time complexityautoCommit to a Big-O in the Complexity Lab.
5. Analyse space complexityautoExtra memory, not the input.
6. Identify the bottleneckautoMeasure your code — where does it bend?
7. OptimiseUsually: a set or dict instead of a scan.
8. Explain why it worksSay it out loud to Solvi.
9. Test the edge casesautoSubmit passes every hidden test.

Python 3.13 · fizzbuzz

def fizzbuzz(n):
    """Return the FizzBuzz strings for 1..n."""
    # Write your solution here
    pass

⌘/Ctrl + Enter runs the examples

Your code runs in real CPython inside your browser — nothing is sent anywhere. The first run downloads the interpreter (about 6 MB, once). Your code is saved on this device as you type.

Complexity Lab

What does this cost as n grows?

Interviewers score the analysis as much as the code. Commit to an answer first — then check it, and measure your code against the optimal one at growing input sizes.

Time complexity of the optimal solution

Space complexity (extra memory)

Pick both to reveal the answer.

Measure it

Runs the function on inputs of size 250 up to 16,000 and records the time and peak memory. Slow solutions stop early — a short curve is itself the answer.

From brute force to optimal

The progression an interviewer wants to hear, one step at a time.

Approach	Time	Space	Idea
Check 15 first	O(n)	O(n)	The most specific condition must come first.

Walkthrough of the optimal approach (try it yourself first)

Loop from 1 to n and test the most specific condition first: divisible by 15 (both 3 and 5), then 3, then 5. Checking 3 first would print "Fizz" for 15.

It's an easy question, but interviewers are watching for clean conditions and an off-by-one-free range.

Complexity: O(n) time, O(n) space. One loop iteration per number, and the output list holds n strings.

Reveal the reference solution

def fizzbuzz(n):
    out = []
    for i in range(1, n + 1):
        if i % 15 == 0:
            out.append("FizzBuzz")
        elif i % 3 == 0:
            out.append("Fizz")
        elif i % 5 == 0:
            out.append("Buzz")
        else:
            out.append(str(i))
    return out

Follow-ups interviewers ask

Add 'Bazz' for multiples of 7 without a pile of elifs.

Frequently asked interview questions

Core interview concepts, complexities, and follow-ups scored by hiring teams.

What is the time complexity of FizzBuzz in Python?

The optimal solution runs in O(n) time and O(n) auxiliary space. One loop iteration per number, and the output list holds n strings.

What follow-up questions do interviewers ask about FizzBuzz in Python?

Add 'Bazz' for multiples of 7 without a pile of elifs.