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FizzBuzz – Solution & Complexity

Interview solutions
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FizzBuzz

Solution Walkthrough

  1. Step 1: Understand the Replacement Rules

    • For every number from 1 through n, return one string.
    • Multiples of 3 become Fizz, multiples of 5 become Buzz.
    • Multiples of both must become FizzBuzz, not just one of the two words.

  2. Step 2: Check the Most Specific Case First

    • A number divisible by both 3 and 5 is divisible by 15.
    • Check this case before checking only 3 or only 5.
    • Otherwise 15 would incorrectly be labeled as just Fizz or just Buzz.
    if num % 15 == 0:
    result.append("FizzBuzz")

  3. Step 3: Loop Through the Range

    • Use range(1, n + 1) because the sequence includes both endpoints: 1 and n.
    • Append the correct string for each number.
    • Convert normal numbers with str(num).
    for num in range(1, n + 1):
    if num % 15 == 0:
        result.append("FizzBuzz")
    elif num % 3 == 0:
        result.append("Fizz")

  4. Step 4: Handle Input Robustly

    • The problem describes n as an integer, but JSON input can sometimes provide numeric-looking values as strings.
    • Converting with int(n) makes the function tolerant of either form.
    • The output remains a list of strings.

  5. Step 5: Complete Solution and Complexity

    • The final solution makes one pass from 1 to n and applies the divisibility rules.
    • Time complexity is O(n).
    • Space complexity is O(n) for the returned list.
    def fizz_buzz(n: int) -> list[str]:
    n = int(n)
    result = []

    for num in range(1, n + 1):
        if num % 15 == 0:
            result.append("FizzBuzz")
        elif num % 3 == 0:
            result.append("Fizz")
        elif num % 5 == 0:
            result.append("Buzz")
        else:
            result.append(str(num))

    return result

FAQ

See also

Practice FizzBuzz online (run code in the browser)Excel Sheet Column Number solution (easy)Integer to Roman solution (medium)Roman to Integer solution (easy)Add Two Numbers solution (medium)All coding interview problems
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