Fizz Buzz

Fizz buzz is a group word game for children to teach them about division. Players take turns to count incrementally, replacing any number divisible by three with the word “fizz”, and any number divisible by five with the word “buzz”.

Fizz buzz has been used as an interview screening device for computer programmers.

Example

A typical round of fizz buzz:

1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, Fizz Buzz, 16, 17, Fizz, 19, Buzz, Fizz, 22, 23, Fizz, Buzz, 26, Fizz, 28, 29, Fizz Buzz, 31, 32, Fizz, 34, Buzz, Fizz, …

Modulus Operator

The modulus operator % is the key to solving fizz buzz.

The modulus operator returns the remainder after an integer division. Here is an example of the modulus operator:

Division	Division Result	Modulus	Modulus Result
1 / 3	0 with a remainder of 3	1 % 3	1
5 / 3	1 with a remainder of 2	5 % 3	2
16 / 3	5 with a remainder of 1	16 % 3	1

A common approach to determine if a number is even or odd is to use the modulus operator:

Modulus	Result	Swift Code	Swift Code Result	Comment
6 % 2	0	let isEven = (number % 2 == 0)	true	If a number is divisible by 2 it is even
5 % 2	1	let isOdd = (number % 2 != 0)	true	If a number is not divisible by 2 it is odd

Solving fizz buzz

Now we can use the modulus operator % to solve fizz buzz.

Finding numbers divisible by three:

Modulus	Modulus Result	Swift Code	Swift Code Result
1 % 3	1	1 % 3 == 0	false
2 % 3	2	2 % 3 == 0	false
3 % 3	0	3 % 3 == 0	true
4 % 3	1	4 % 3 == 0	false

Finding numbers divisible by five:

Modulus	Modulus Result	Swift Code	Swift Code Result
1 % 5	1	1 % 5 == 0	false
2 % 5	2	2 % 5 == 0	false
3 % 5	3	3 % 5 == 0	false
4 % 5	4	4 % 5 == 0	false
5 % 5	0	5 % 5 == 0	true
6 % 5	1	6 % 5 == 0	false

The code

Here is a simple implementation in Swift:

func fizzBuzz(_ numberOfTurns: Int) {
  for i in 1...numberOfTurns {
    var result = ""

    if i % 3 == 0 {
      result += "Fizz"
    }

    if i % 5 == 0 {
      result += (result.isEmpty ? "" : " ") + "Buzz"
    }

    if result.isEmpty {
      result += "\(i)"
    }

    print(result)
  }
}

Put this code in a playground and test it like so:

fizzBuzz(15)

This will output:

1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, Fizz Buzz

See also

Fizz buzz on Wikipedia

Written by Chris Pilcher