Ternary expression

Leap
Leap in Scala 
object Leap {
  def leapYear(year: Int): Boolean =
    if (year % 100 == 0) year % 400 == 0
    else year % 4 == 0
}

A ternary expression 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 ternary expression 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 ternary expression 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, the ternary expression tests an outlier condition first, making it less efficient than another approach that would first test if the year is evenly divisible by 4, which is more likely than the year being evenly divisible by 100.

9th Oct 2024 · Found it useful?

Other Approaches to Leap in Scala

Other ways our community solved this exercise
def leapYear(year: Int): Boolean =
  year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)
Boolean chain

Use a chain of boolean expressions. 

def leapYear(year: Int): Boolean =
  (year % 4, year % 100, year % 400) match {
    case (_, _, 0) => true
    case (_, 0, _) => false
    case (0, _, _) => true
    case (_, _, _) => false
  }
match on a tuple

Use a match on a tuple made from boolean expressions. 

import java.time.{LocalDate, Month}

object Leap {
  def leapYear(year: Int): Boolean =
    LocalDate.of(year, Month.FEBRUARY, 28).plusDays(1).getDayOfMonth() == 29
}
LocalDate plusDays

Use LocalDate plusDays. 

import java.time.{Year}

object Leap {
  def leapYear(year: Int): Boolean =
    Year.of(year).isLeap()
}
Built-in method

Use the built-in method.