Add 2023 Day 09 solutions

palinkiewicz · palinkiewicz · commit 33518c4cc184 · 2023-12-09T09:59:54.000+01:00
diff --git a/adventofcode2023/Day09.kt b/adventofcode2023/Day09.kt
@@ -0,0 +1,26 @@
+package adventofcode2023
+
+import java.io.File
+
+object Day09 {
+    private fun getPrediction(values: List<Int>, end: Boolean = true): Int {
+        return if (values.all { it == 0 }) 0
+        else if (end) values.last() + getPrediction(values.zipWithNext { a, b -> b - a })
+        else values.first() - getPrediction(values.zipWithNext { a, b -> b - a }, end = false)
+    }
+
+    fun part1(inputs: List<List<Int>>) = println(inputs.sumOf { getPrediction(it) })
+
+    fun part2(inputs: List<List<Int>>) = println(inputs.sumOf { getPrediction(it, end = false) })
+}
+
+fun main() {
+    val inputs = File("resources/adventofcode2023/Day09.txt")
+        .readLines()
+        .map { line ->
+            line.split(" ").map { it.toInt() }
+        }
+
+    Day09.part1(inputs)
+    Day09.part2(inputs)
+}
