Solution 2018-02 (Inventory Management System)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2018/day02/InventoryManagementSystem.kt

@@ -0,0 +1,59 @@
+package de.ronny_h.aoc.year2018.day02
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.combinations
+import kotlin.math.min
+
+fun main() = InventoryManagementSystem().run("5434", "agimdjvlhedpsyoqfzuknpjwt")
+
+class InventoryManagementSystem : AdventOfCode<String>(2018, 2) {
+    override fun part1(input: List<String>): String {
+        var twoLetterCount = 0
+        var threeLetterCount = 0
+        input.forEach { id ->
+            val groups = id.groupBy { it }
+            twoLetterCount += if (groups.any { it.value.size == 2 }) 1 else 0
+            threeLetterCount += if (groups.any { it.value.size == 3 }) 1 else 0
+        }
+        return "${twoLetterCount * threeLetterCount}"
+    }
+
+    override fun part2(input: List<String>): String {
+        val minPair = input
+            .combinations()
+            .minBy { lev(it.first, it.second) }
+
+        return minPair.first.filterIndexed { i, char ->
+            minPair.second[i] == char
+        }
+    }
+}
+
+private val levCache = mutableMapOf<Pair<String, String>, Int>()
+
+/**
+ * The Levenshtein distance (an edit distance).
+ */
+fun lev(a: String, b: String): Int {
+    levCache[a to b]?.let { return it }
+
+    if (b.isEmpty()) return a.length
+    if (a.isEmpty()) return b.length
+
+    val aTail = a.substring(1)
+    val bTail = b.substring(1)
+
+    val tailResult = lev(aTail, bTail)
+    levCache[aTail to bTail] = tailResult
+
+    if (a.first() == b.first()) {
+        return tailResult
+    }
+
+    val aTailResult = lev(aTail, b)
+    val bTailResult = lev(a, bTail)
+    levCache[aTail to b] = aTailResult
+    levCache[a to bTail] = bTailResult
+
+    return 1 + min(min(aTailResult, bTailResult), tailResult)
+}

src/test/kotlin/de/ronny_h/aoc/year2018/day02/InventoryManagementSystemTest.kt

@@ -0,0 +1,51 @@
+package de.ronny_h.aoc.year2018.day02
+
+import de.ronny_h.aoc.extensions.asList
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.data.forAll
+import io.kotest.data.row
+import io.kotest.matchers.shouldBe
+
+class InventoryManagementSystemTest : StringSpec({
+
+    "part 1: the checksum (product of number of letters appearing twice and 3 times exactly)" {
+        val input = """
+            abcdef
+            bababc
+            abbcde
+            abcccd
+            aabcdd
+            abcdee
+            ababab
+        """.asList()
+
+        InventoryManagementSystem().part1(input) shouldBe "12"
+    }
+
+    "part 2: the common letters between the two correct box IDs" {
+        val input = """
+            abcde
+            fghij
+            klmno
+            pqrst
+            fguij
+            axcye
+            wvxyz
+        """.asList()
+        InventoryManagementSystem().part2(input) shouldBe "fgij"
+    }
+
+    "The Levenshtein distance" {
+        forAll(
+            row("", "", 0),
+            row("", "a", 1),
+            row("a", "", 1),
+            row("abc", "abc", 0),
+            row("abc", "a_c", 1),
+            row("abc", "xyz", 3),
+            row("abc", "abcxyz", 3),
+        ) { a, b, distance ->
+            lev(a, b) shouldBe distance
+        }
+    }
+})