Boolean chain

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 {
	return  year%4 == 0 && (year%100 != 0 || year%400 == 0)
}

The first boolean expression uses the modulus operator to check if the year is evenly divided by 4.

  • If the year is not evenly divisible by 4, then the chain will "short circuit" due to the next operator being a logical AND (&&), and will return false.
  • If the year is evenly divisible by 4, then the year is checked to not be evenly divisible by 100.
  • If the year is not evenly divisible by 100, then the expression is true and the chain will "short-circuit" to return true, since the next operator is a logical OR (||).
  • If the year is evenly divisible by 100, then the expression is false, and the returned value from the chain will be if the year is evenly divisible by 400.

This approach exhausts after a maximum of three checks.

year year % 4 == 0 year % 100 != 0 year % 400 == 0 is leap year
2020 true true not evaluated true
2019 false not evaluated not evaluated false
2000 true false true true
1900 true false false false
7th Aug 2024 · Found it useful?

Other Approaches to Leap in Go

Other ways our community solved this exercise
func IsLeapYear(year int) bool {
	if year%100 == 0 {
		return year%400 == 0
	} else {
		return year%4 == 0
	}
}
Maximum two checks

Use a maximum of two checks. 

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().