Solution 2015-08 (Matchsticks)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2015/day08/Matchsticks.kt

@@ -0,0 +1,30 @@
+package de.ronny_h.aoc.year2015.day08
+
+import de.ronny_h.aoc.AdventOfCode
+
+fun main() = Matchsticks().run(1350, 2085)
+
+class Matchsticks : AdventOfCode<Int>(2015, 8) {
+    override fun part1(input: List<String>): Int =
+        input.sumOf { numberOfCharactersOfCode(it) - numberOfCharactersInMemory(it) }
+
+    override fun part2(input: List<String>): Int =
+        input.sumOf { numberOfCharactersEncoded(it) - numberOfCharactersOfCode(it) }
+
+    fun numberOfCharactersOfCode(string: String) = string.length
+    fun numberOfCharactersInMemory(string: String) = string.unescape().length
+    fun numberOfCharactersEncoded(string: String) = string.length +
+            string.count { it == '"' } +
+            string.count { it == '\\' } +
+            2
+}
+
+private val startQuotationRegex = "^\"".toRegex()
+private val endQuotationRegex = "\"$".toRegex()
+private val asciiCharRegex = "\\\\x[0-9A-Fa-f][0-9A-Fa-f]".toRegex()
+
+fun String.unescape(): String = replace(startQuotationRegex, "")
+    .replace(endQuotationRegex, "")
+    .replace(asciiCharRegex, """_""")
+    .replace("""\"""", """"""")
+    .replace("""\\""", """\""")

src/test/kotlin/de/ronny_h/aoc/year2015/day08/MatchsticksTest.kt

@@ -0,0 +1,79 @@
+package de.ronny_h.aoc.year2015.day08
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.data.forAll
+import io.kotest.data.row
+import io.kotest.matchers.shouldBe
+
+class MatchsticksTest : StringSpec({
+
+    "the number of characters of code" {
+        val matchsticks = Matchsticks()
+        forAll(
+            row("""""""", 2),
+            row(""""abc"""", 5),
+            row(""""aaa\"aaa"""", 10),
+            row(""""\x27"""", 6),
+            row(""""\\"""", 4),
+            row(""""\\\\"""", 6),
+            row(""""\\\\""""", 7),
+        ) { string, expected ->
+            matchsticks.numberOfCharactersOfCode(string) shouldBe expected
+        }
+    }
+
+    "the number of characters of the in-memory string" {
+        val matchsticks = Matchsticks()
+        forAll(
+            row("""""""", 0),
+            row(""""abc"""", 3),
+            row(""""aaa\"aaa"""", 7),
+            row(""""\x27"""", 1),
+            row(""""\\x27"""", 2),
+            row(""""\\"""", 1),
+            row(""""\\\\"""", 2),
+            row(""""\\\\""""", 3),
+            row(""""\\\""""", 2),
+            row(""""\\""""", 2),
+        ) { string, expected ->
+            matchsticks.numberOfCharactersInMemory(string) shouldBe expected
+        }
+    }
+
+    "unescape ascii characters from hexadecimal escapes" {
+        """"\x27"""".unescape() shouldBe """_"""
+        """"\xb7"""".unescape() shouldBe """_"""
+    }
+
+    "part 1: the total number of code chars minus number of in-memory chars" {
+        val input = listOf(
+            """""""",
+            """"abc"""",
+            """"aaa\"aaa"""",
+            """"\x27"""",
+        )
+        Matchsticks().part1(input) shouldBe 12
+    }
+
+    "the number of characters of encoded string" {
+        val matchsticks = Matchsticks()
+        forAll(
+            row("""""""", 6),
+            row(""""abc"""", 9),
+            row(""""aaa\"aaa"""", 16),
+            row(""""\x27"""", 11),
+        ) { string, expected ->
+            matchsticks.numberOfCharactersEncoded(string) shouldBe expected
+        }
+    }
+
+    "part 2: the total number of newly encoded chars minus number of code chars" {
+        val input = listOf(
+            """""""",
+            """"abc"""",
+            """"aaa\"aaa"""",
+            """"\x27"""",
+        )
+        Matchsticks().part2(input) shouldBe 19
+    }
+})