2023 - Day09 - for part 2 - just reverse the strings in part 1

fmmr · Dec 9, 2023 · 423e835 · 423e835
1 parent cc9f6ef
commit 423e835
Showing 1 changed file with 4 additions and 6 deletions.
diff --git a/src/main/kotlin/no/rodland/advent_2023/Day09.kt b/src/main/kotlin/no/rodland/advent_2023/Day09.kt
@@ -14,16 +14,14 @@ class Day09(val input: List<String>) : Day<Int, Int, List<List<Int>>> {
     }
 
     override fun partTwo(): Int {
-        return parsed.sumOf { it.previous() }
+        return parsed.map { it.reversed() }.sumOf { it.next() }
     }
 
     private fun List<Int>.next(): Int = if (all { it == 0 }) 0
-    else last() + diffs().next()
+    else last() + zipWithNext { a, b -> b - a }.next()
 
-    private fun List<Int>.previous(): Int = if (all { it == 0 }) 0
-    else first() - diffs().previous()
-
-    private fun List<Int>.diffs(): List<Int> = zipWithNext { a, b -> b - a }
+//    private fun List<Int>.previous(): Int = if (all { it == 0 }) 0
+//    else first() - diffs().previous()
 
     override fun List<String>.parse(): List<List<Int>> {
         return map { line ->