2024 - Day 09 - part 1

fmmr · Dec 9, 2024 · e0219c6 · e0219c6
1 parent 80aa559
commit e0219c6
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Showing 2 changed files with 40 additions and 11 deletions.
diff --git a/src/main/kotlin/no/rodland/advent_2024/Day09.kt b/src/main/kotlin/no/rodland/advent_2024/Day09.kt
@@ -5,27 +5,55 @@ import no.rodland.advent.Day
 // template generated: 09/12/2024
 // Fredrik Rødland 2024
 
-class Day09(val input: List<String>) : Day<Long, Long, Pair<List<Int>, List<Int>>> {
+class Day09(val input: List<String>) : Day<Long, Long, Pair<Int, List<Day09.Num?>>> {
 
     private val parsed = input.parse()
-    private val files = parsed.first
-    private val space = parsed.second
+    val size = parsed.first
+    val parsedList = parsed.second
 
     override fun partOne(): Long {
-        parsed
-        return 2
+        val list = parsedList.toMutableList()
+        val memory = (0..<size).map { idx ->
+            list[idx] ?: list.removeLastNonNull()
+        }
+        return memory.map { it.id }.checksum()
+    }
+
+    private fun MutableList<Num?>.removeLastNonNull(): Num {
+        var last = removeLast()
+        while (last == null) {
+            last = removeLast()
+        }
+        return last
     }
 
+    private fun Iterable<Int>.checksum(): Long = foldIndexed(0L) { i, acc, id -> acc + i * id }
+
     override fun partTwo(): Long {
         return 2
     }
 
-    override fun List<String>.parse(): Pair<List<Int>, List<Int>> {
-        return first()
+    override fun List<String>.parse(): Pair<Int, List<Num?>> {
+        var id = 0
+        var size = 0
+        val chunked = first()
             .map { c -> c.digitToInt() }
-            .chunked(2) { it.first() to it.last() }
-            .unzip()
+            .chunked(2) {
+                val num = Num(id++, it.first())
+                size += it.first()
+                if (it.size == 2) {
+                    num to it.last()
+                } else {
+                    num to null
+                }
+            }
+        val flatMap = chunked.flatMap { (num, space) ->
+            (0..<num.size).map { num } + (space?.let { (0..<space).map { null } } ?: emptyList())
+        }
+        return size to flatMap
     }
 
+    data class Num(val id: Int, val size: Int)
+
     override val day = "09".toInt()
 }
diff --git a/src/test/kotlin/no/rodland/advent_2024/Day09Test.kt b/src/test/kotlin/no/rodland/advent_2024/Day09Test.kt
@@ -15,9 +15,9 @@ internal class Day09Test {
     private val data09 = "2024/input_09.txt".readFile()
     private val test09 = "2024/input_09_test.txt".readFile()
 
-    private val resultTestOne = 2L
+    private val resultTestOne = 1928L
     private val resultTestTwo = 2L
-    private val resultOne = 2L
+    private val resultOne = 6421128769094L
     private val resultTwo = 2L
 
     val test = defaultTestSuiteParseOnInit(
@@ -29,6 +29,7 @@ internal class Day09Test {
         resultTwo,
         { Day09(data09) },
         { Day09(test09) },
+        numTestPart1 = 200
     )
 
     @Nested