DayOne.kt

package com.morninghacks.aoc2017

fun captcha(input: String): Int {
    val ints = input.map { Character.getNumericValue(it) }
    var sum = 0
    for ((index, current) in ints.withIndex()) {
        val next = if (index == ints.size - 1) ints[0] else ints[index + 1]
        sum += if (current == next) current else 0
    }
    return sum
}

fun functionalCaptcha(input: String): Int {
    class Accum(val sum: Int = 0, val previousDigit: Int = Int.MIN_VALUE)

    val ints = (input + input[0]).map { Character.getNumericValue(it) }
    return ints.fold(Accum(), { acc, curr ->
        if (acc.previousDigit == curr) Accum(acc.sum + curr, curr)
        else Accum(acc.sum, curr)
    }).sum

}

fun main(args: Array<String>) {
    val myCaptcha = "61697637962276641366442297247367117738114719863473648131982449728688116728695866572989524473392982963976411147683588415878214189996163533584547175794158118148724298832798898333399786561459152644144669959887341481968319172987357989785791366732849932788343772112176614723858474959919713855398876956427631354172668133549845585632211935573662181331613137869866693259374322169811683635325321597242889358147123358117774914653787371368574784376721652181792371635288376729784967526824915192526744935187989571347746222113625577963476141923187534658445615596987614385911513939292257263723518774888174635963254624769684533531443745729344341973746469326838186248448483587477563285867499956446218775232374383433921835993136463383628861115573142854358943291148766299653633195582135934544964657663198387794442443531964615169655243652696782443394639169687847463721585527947839992182415393199964893658322757634675274422993237955354185194868638454891442893935694454324235968155913963282642649968153284626154111478389914316765783434365458352785868895582488312334931317935669453447478936938533669921165437373741448378477391812779971528975478298688754939216421429251727555596481943322266289527996672856387648674166997731342558986575258793261986817177487197512282162964167151259485744835854547513341322647732662443512251886771887651614177679229984271191292374755915457372775856178539965131319568278252326242615151412772254257847413799811417287481321745372879513766235745347872632946776538173667371228977212143996391617974367923439923774388523845589769341351167311398787797583543434725374343611724379399566197432154146881344528319826434554239373666962546271299717743591225567564655511353255197516515213963862383762258959957474789718564758843367325794589886852413314713698911855183778978722558742329429867239261464773646389484318446574375323674136638452173815176732385468675215264736786242866295648997365412637499692817747937982628518926381939279935993712418938567488289246779458432179335139731952167527521377546376518126276"
    println(captcha(myCaptcha))
}

DayOneSpec.kt

ackage com.morninghacks.aoc2017

import org.jetbrains.spek.api.Spek
import org.jetbrains.spek.api.dsl.given
import org.jetbrains.spek.api.dsl.it
import org.jetbrains.spek.api.dsl.on
import kotlin.test.assertEquals


object Day01Spec : Spek({
    given("Day One : Part One") {
        val dataProvider = mapOf("1122" to 3,
                "1111" to 4,
                "1234" to 0,
                "91212129" to 9)


        on("captcha") {
            for ((input, expected) in dataProvider) {
                it("should produce $expected") {
                    assertEquals(expected, captcha(input))
                }
            }
        }

        on("functionalCaptcha") {
            for ((input, expected) in dataProvider) {
                it("should produce $expected") {
                    assertEquals(expected, functionalCaptcha(input))
                }
            }
        }
}