Day03.kt

fun manhattan(x: Int): Int {
    val y = nextOddPerfectSquareInclusive(x)
    val max = sqrt(y.toDouble()).roundToInt() - 1
    val min = max / 2
    val f = if (max == 0) 0 else max - ((y - x) % max) //for 33, f is 2, needs to be 4
    return if (f < min) max - f else f
}

fun nextOddPerfectSquareInclusive(x: Int): Int {
    for (i in 1..x step 2) {
        val iSquared = Math.pow(i.toDouble(), 2.toDouble()).roundToInt()
        val nextSquared = Math.pow((i + 2).toDouble(), 2.toDouble()).roundToInt()

        if (x == iSquared) return x
        else if (x > iSquared && x < nextSquared) return nextSquared
        else continue
    }
    throw IllegalStateException()
}

Day03Spec.kt

object Day03Spec : Spek({
    given("Day Three : Part One") {
        val testData = mapOf(1 to 0, 9 to 2, 10 to 3, 12 to 3, 23 to 2, 27 to 4, 33 to 4, 35 to 4, 40 to 3, 47 to 4, 48 to 5,1024 to 31)
        on("manhattan") {
            for ((input, expected) in testData) {
                it("should return $expected when given input of $input") {
                    assertEquals(expected, manhattan(input))
                }
            }
        }
    }
})