Maximum two checks

Leap
Leap in Go 
// Package leap is a small library for determing if the passed in year is a leap year.
package leap

// IsLeapYear returns if the passed in year is a leap year.
func IsLeapYear(year int) bool {
	if year%100 == 0 {
		return year%400 == 0
	} else {
		return year%4 == 0
	}
}

This approach uses a maximum of two checks to determine if a year is a leap year.

It starts by testing the outlier condition of the year being evenly divisible by 100. It does this by using the modulus operator. If the year is evenly divisible by 100, then the expression is true, and the function returns if the year is evenly divisible by 400. If the year is not evenly divisible by 100, then the expression is false, and the function returns if the year is evenly divisible by 4.

year year % 100 == 0 year % 400 == 0 year % 4 == 0 is leap year
2020 false not evaluated true true
2019 false not evaluated false false
2000 true true not evaluated true
1900 true false not evaluated false

Although it uses a maximum of only two checks, this approach tests an outlier condition of the year being evenly divisible by 100 first, which is less likely than the year being evenly divisible by 4.

11th Sep 2024 · Found it useful?

Other Approaches to Leap in Go

Other ways our community solved this exercise
// Package leap is a small library for determing if the passed in year is a leap year.
package leap

// IsLeapYear returns if the passed in year is a leap year.
func IsLeapYear(year int) bool {
	return  year%4 == 0 && (year%100 != 0 || year%400 == 0)
}
Boolean chain

Use a chain of boolean expressions. 

package leap

import "time"

// IsLeapYear returns if the passed in year is a leap year.
func IsLeapYear(year int) bool {
	return time.Date(year, time.February, 28, 0, 0, 0, 0, time.UTC).Add(time.Duration(time.Hour*24)).Day() == 29
}
time addition

Use time addition. 

package leap

import "time"

// IsLeapYear returns if the passed in year is a leap year.
func IsLeapYear(year int) bool {
	return time.Date(year, time.December, 31, 0, 0, 0, 0, time.UTC).YearDay() == 366
}
time.YearDay()

Use time YearDay().