FizzBuzz

The smallest interesting program in the world, and the reason it survives as an exercise: it needs three branches, and the order you write them in decides whether it is right.

Go's if takes a bool and nothing else. There is no truthiness, so if n is a compile error and if n != 0 is what you meant. The condition needs no parentheses, and the braces are never optional:

if n%3 == 0 {
	return "Fizz"
} else if n%5 == 0 {
	return "Buzz"
}

% is the remainder operator. In Go the result takes the sign of the left operand, so -7 % 3 is -1 and 7 % -3 is 1. That only matters here because n % 3 == 0 is true for negative multiples too, which is what the tests expect.

Task

Finish the three functions in main.go.

1. FizzBuzz(n int) string classifies one number: "FizzBuzz" when it divides by both 3 and 5, "Fizz" for 3, "Buzz" for 5, and otherwise the number's digits as a string. FizzBuzz(7) is "7".
2. FizzBuzzUpTo(n int) []string returns FizzBuzz(1) through FizzBuzz(n) in order. An n below 1 gives a slice with no elements.
3. IsLeapYear(y int) bool applies the Gregorian rule: divisible by 4, except divisible by 100, except divisible by 400. 2000 is a leap year and 1900 is not.

Hints

• Check the combined case first. 15 % 3 is 0, so a Fizz branch above the FizzBuzz branch answers "Fizz" and the right answer never gets a turn. n%15 == 0 and n%3 == 0 && n%5 == 0 are the same test; pick the one you find clearer.
• Turning an int into its digits is strconv.Itoa(n). string(n) compiles and is wrong: it produces the character with that code point. fmt.Sprint(n) works too and costs more.
• strconv is not imported yet. Add it; an unused import is a compile error, which is why the starter does not carry one you might not need.
• Build the slice with append on a starting out := []string{}. The tests only check the length, so nil would pass too, but an empty non-nil slice is the friendlier thing to hand back.
• The leap-year rule is three tests in a specific order: 400 first, then 100, then 4. Written in any other order it is either wrong or much longer.