The challenge

Given a set of numbers, return the additive inverse of each. Each positive becomes negatives, and the negatives become positives.

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invert([1,2,3,4,5]) == [-1,-2,-3,-4,-5]
invert([1,-2,3,-4,5]) == [-1,2,-3,4,-5]
invert([]) == []

The solution in Kotlin code

Option 1:

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fun invert(arr: IntArray) = arr.map { -it }.toIntArray()

Option 2:

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fun invert(arr: IntArray): IntArray {
    return IntArray(arr.size){ -arr[it] }
}

Option 3:

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fun invert(arr: IntArray): IntArray {
    var x = 0
    while (x < arr.size) {
        arr[x] = arr[x] * -1
        x++
    }
    return arr
}

Test cases to validate our solution

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import org.junit.Assert.*;
import org.junit.Test

class TestExample {
  @Test
  fun testFixed() {
    assertArrayEquals(intArrayOf(-1,-2,-3,-4,-5), invert(intArrayOf(1,2,3,4,5)))
    assertArrayEquals(intArrayOf(-1,2,-3,4,-5), invert(intArrayOf(1,-2,3,-4,5)))
    assertArrayEquals(intArrayOf(), invert(intArrayOf()))
    assertArrayEquals(intArrayOf(0), invert(intArrayOf(0)))
  }
}