412. Fizz Buzz

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Reformulated question¶

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

"FizzBuzz" if the number is divisible by 15
"Fizz" if divisible by 3
"Buzz" if divisible by 5
otherwise the number itself as a string

Compact example:

n = 6 -> ["1", "2", "Fizz", "4", "Buzz", "Fizz"]

Key trick¶

Check the combined case first:

divisibility by 15
then 3
then 5

This avoids incorrectly returning "Fizz" or "Buzz" for multiples of both.

Trap¶

Common mistakes:

checking 3 and 5 before 15
using 0..n-1 instead of 1..n
returning integers instead of strings

Why this question is interesting¶

It is simple but tests:

careful condition ordering
off-by-one handling
clean loop and string construction

Solve the problem with idiomatic python¶

class Solution:
    def fizzBuzz(self, n: int) -> list[str]:
        answer = []

        # Build the result from 1 to n inclusive.
        for i in range(1, n + 1):
            if i % 15 == 0:
                answer.append("FizzBuzz")
            elif i % 3 == 0:
                answer.append("Fizz")
            elif i % 5 == 0:
                answer.append("Buzz")
            else:
                answer.append(str(i))

        return answer

Library alternative:

None worth using here; the direct loop is the exact intended solution.

Pytest test¶

import pytest

@pytest.mark.parametrize(
    ("n", "expected"),
    [
        (1, ["1"]),
        (3, ["1", "2", "Fizz"]),
        (5, ["1", "2", "Fizz", "4", "Buzz"]),
        (15, [
            "1", "2", "Fizz", "4", "Buzz",
            "Fizz", "7", "8", "Fizz", "Buzz",
            "11", "Fizz", "13", "14", "FizzBuzz",
        ]),
        (16, [
            "1", "2", "Fizz", "4", "Buzz",
            "Fizz", "7", "8", "Fizz", "Buzz",
            "11", "Fizz", "13", "14", "FizzBuzz", "16",
        ]),
    ],
)
def test_fizz_buzz(n, expected):
    assert Solution().fizzBuzz(n) == expected

Comment my solution¶

No solution was provided to review.

Code¶

import pytest


class Solution:
    def fizzBuzz(self, n: int) -> list[str]:
        answer = []

        # Build the result from 1 to n inclusive.
        for i in range(1, n + 1):
            if i % 15 == 0:
                answer.append("FizzBuzz")
            elif i % 3 == 0:
                answer.append("Fizz")
            elif i % 5 == 0:
                answer.append("Buzz")
            else:
                answer.append(str(i))

        return answer


@pytest.mark.parametrize(
    ("n", "expected"),
    [
        (1, ["1"]),
        (3, ["1", "2", "Fizz"]),
        (5, ["1", "2", "Fizz", "4", "Buzz"]),
        (15, [
            "1", "2", "Fizz", "4", "Buzz",
            "Fizz", "7", "8", "Fizz", "Buzz",
            "11", "Fizz", "13", "14", "FizzBuzz",
        ]),
        (16, [
            "1", "2", "Fizz", "4", "Buzz",
            "Fizz", "7", "8", "Fizz", "Buzz",
            "11", "Fizz", "13", "14", "FizzBuzz", "16",
        ]),
    ],
)
def test_fizz_buzz(n, expected):
    assert Solution().fizzBuzz(n) == expected


Solution().fizzBuzz(3)
Solution().fizzBuzz(5)
Solution().fizzBuzz(15)