Solution 2015-10 (Elves Look, Elves Say)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2015/day10/ElvesLookElvesSay.kt

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+package de.ronny_h.aoc.year2015.day10
+
+import de.ronny_h.aoc.AdventOfCode
+
+fun main() = ElvesLookElvesSay().run(329356, 4666278)
+
+class ElvesLookElvesSay : AdventOfCode<Int>(2015, 10) {
+
+    override fun part1(input: List<String>) = input.first().lookAndSay(40)
+    override fun part2(input: List<String>) = input.first().lookAndSay(50)
+
+    private fun String.lookAndSay(times: Int): Int {
+        var sequence = this
+        repeat(times) {
+            sequence = lookAndSay(sequence)
+        }
+        return sequence.length
+    }
+
+    fun lookAndSay(sequence: String): String {
+        var char = sequence.first()
+        var count = 0
+        return sequence.map {
+            if (it == char) {
+                count++
+                ""
+            } else {
+                val s = "$count$char"
+                char = it
+                count = 1
+                s
+            }
+        }.joinToString("") + "$count$char"
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year2015/day10/ElvesLookElvesSayTest.kt

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+package de.ronny_h.aoc.year2015.day10
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class ElvesLookElvesSayTest : StringSpec({
+
+    val day10 = ElvesLookElvesSay()
+
+    "1 becomes 11" {
+        day10.lookAndSay("1") shouldBe "11"
+    }
+
+    "11 becomes 21" {
+        day10.lookAndSay("11") shouldBe "21"
+    }
+
+    "21 becomes 1211" {
+        day10.lookAndSay("21") shouldBe "1211"
+    }
+
+    "1211 becomes 111221" {
+        day10.lookAndSay("1211") shouldBe "111221"
+    }
+
+    "111221 becomes 312211" {
+        day10.lookAndSay("111221") shouldBe "312211"
+    }
+
+    "part 1: The length of 40 times lookAndSay for 1" {
+        day10.part1(listOf("1")) shouldBe 82350
+    }
+
+    "part 2: The length of 50 times lookAndSay for 1" {
+        day10.part2(listOf("1")) shouldBe 1166642
+    }
+})