Solution 2015-01 (Not Quite Lisp)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year15/day01/NotQuiteLisp.kt

@@ -0,0 +1,30 @@
+package de.ronny_h.aoc.year15.day01
+
+import de.ronny_h.aoc.AdventOfCode
+
+fun main() = NotQuiteLisp().run(232, 1783)
+
+class NotQuiteLisp : AdventOfCode<Int>(2015, 1) {
+    override fun part1(input: List<String>): Int {
+        require(input.size == 1)
+        val instructions = input.first()
+        val ups = instructions.count { it == '(' }
+        val downs = instructions.count { it == ')' }
+        return ups - downs
+    }
+
+    override fun part2(input: List<String>): Int {
+        var floor = 0
+        input.first().forEachIndexed { i, char ->
+            when (char) {
+                '(' -> floor++
+                ')' -> floor--
+                else -> error("invalid instruction: $char at position $i")
+            }
+            if (floor < 0) {
+                return i + 1
+            }
+        }
+        return 0
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year15/day01/NotQuiteLispTest.kt

@@ -0,0 +1,26 @@
+package de.ronny_h.aoc.year15.day01
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.data.forAll
+import io.kotest.data.row
+import io.kotest.matchers.shouldBe
+
+class NotQuiteLispTest : StringSpec({
+    "part 1: find the right floor by counting parenthesis" {
+        forAll(
+            row("(())", 0),
+            row("()()", 0),
+            row("(((", 3),
+            row("(()(()(", 3),
+            row("))(((((", 3),
+            row(")())())", -3),
+        ) { input, result ->
+            NotQuiteLisp().part1(listOf(input)) shouldBe result
+        }
+    }
+
+    "part 2: the fist position leading to a basement floor" {
+        NotQuiteLisp().part2(listOf(")")) shouldBe 1
+        NotQuiteLisp().part2(listOf("()())")) shouldBe 5
+    }
+})