Leap: implement basis

[bitfield]

This is a common side exercise, probably because it looks (and is) pretty simple. Some people even attempt this before Two Fer.

Every solution, without exception, looks like this:

func IsLeapYear(year int) bool {
	return (year%4 == 0 && year%100 != 0) || year%400 == 0
}

(or some equivalent Boolean transformation). Fine as far as it goes, but there's a missed opportunity to make this code clear, simple, and readable, in a way that matches the English description of the problem. Something along these lines:

func IsLeapYear(year int) bool {
	if year%4 != 0 {
		return false
	}
	if year%400 == 0 {
		return true
	}
	if year%100 == 0 {
		return false
	}
	return true
}

(Not saying this is the perfect solution, but it illustrates what I'm talking about.)