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

Alternatively, Swift's built in function .isMultiple(of:) can be used, i.e. 6.isMultiple(of: 2) will return true, 5.isMultiple(of: 2) will return false

Solving fizz buzz

Now we can use the modulus operator % or .isMultiple(of:) method to solve fizz buzz.

Finding numbers divisible by three:

Modulus	Modulus Result	Swift Code using Modulo	Swift Code using .isMultiple(of:)	Swift Code Result
1 % 3	1	`1 % 3 == 0`	`1.isMultiple(of: 3)`	`false`
2 % 3	2	`2 % 3 == 0`	`2.isMultiple(of: 3)`	`false`
3 % 3	0	`3 % 3 == 0`	`3.isMultiple(of: 3)`	`true`
4 % 3	1	`4 % 3 == 0`	`4.isMultiple(of: 3)`	`false`

Finding numbers divisible by five:

Modulus	Modulus Result	Swift Code using Modulo	Swift Code using .isMultiple(of:)	Swift Code Result
1 % 5	1	`1 % 5 == 0`	`1.isMultiple(of: 5)`	`false`
2 % 5	2	`2 % 5 == 0`	`2.isMultiple(of: 5)`	`false`
3 % 5	3	`3 % 5 == 0`	`3.isMultiple(of: 5)`	`false`
4 % 5	4	`4 % 5 == 0`	`4.isMultiple(of: 5)`	`false`
5 % 5	0	`5 % 5 == 0`	`5.isMultiple(of: 5)`	`true`
6 % 5	1	`6 % 5 == 0`	`6.isMultiple(of: 5)`	`false`

The code

Here is a simple implementation in Swift using Modulus approach

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)
  }
}

Here is simple implementation in Swift using .isMultiple(of:) and switch statement

func fizzBuzz(_ numberOfTurns: Int) {
    guard numberOfTurns >= 1 else {
        print("Number of turns must be >= 1")
        return
    }
    
    for i in 1...numberOfTurns {
        switch (i.isMultiple(of: 3), i.isMultiple(of: 5)) {
        case (false, false):
            print("\(i)")
        case (true, false):
            print("Fizz")
        case (false, true):
            print("Buzz")
        case (true, true):
            print("Fizz Buzz")
        }
    }
}

Put either 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

Originally written by Chris Pilcher
Updated by Lance Rettberg