Ternary expression

Leap
Leap in Kotlin

Ternary expression

data class Year(val year: Int) {
    val isLeap = 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.

8th May 2024 · Found it useful?

Other Approaches to Leap in Kotlin

Other ways our community solved this exercise
data class Year(val year: Int) {
    val isLeap = year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)
}
Boolean chain

Use a chain of boolean expressions. 

import java.time.*

data class Year(val year: Int) {
    val isLeap = LocalDate.of(year, Month.FEBRUARY, 28).plusDays(1).dayOfMonth == 29
}
plusDays method

Use the plusDays method. 

import java.time.*

data class Year(val year: Int) {
    val isLeap = LocalDate.of(year, Month.FEBRUARY, 28).isLeapYear
}
Built-in method

Use the built-in method.