Boolean chain

Leap
Leap in Scala 
object Leap {
  def leapYear(year: Int): Boolean =
    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.
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

The chain of boolean expressions is efficient, as it proceeds from testing the most likely to least likely conditions.

9th Oct 2024 · Found it useful?

Other Approaches to Leap in Scala

Other ways our community solved this exercise
def leapYear(year: Int): Boolean =
  if (year % 100 == 0) year % 400 == 0
  else year % 4 == 0
Ternary expression

Use a ternary expression of boolean conditions. 

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.