From 6bc6836314c1af78a455cbddcf36ef319ae7605e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fredrik=20R=C3=B8dland?= <fmr@finn.no>
Date: Fri, 6 Dec 2024 00:24:26 +0100
Subject: [PATCH] 2024 Day 05 part 2 re-written to not sort twice.

---
 src/main/kotlin/no/rodland/advent_2024/Day05.kt | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/main/kotlin/no/rodland/advent_2024/Day05.kt b/src/main/kotlin/no/rodland/advent_2024/Day05.kt
index 5618a7bc..aa4813c6 100644
--- a/src/main/kotlin/no/rodland/advent_2024/Day05.kt
+++ b/src/main/kotlin/no/rodland/advent_2024/Day05.kt
@@ -26,10 +26,13 @@ class Day05(val input: List<String>) : Day<Int, Int, Pair<Map<Int, Set<Int>>, Li
     }
 
     override fun partTwo(): Int {
-        return pages
-            .filterNot { it.valid() }
-            .map { it.sort() }
-            .sumOf { it[it.size / 2] }
+        // only sorting once
+        return pages.map { it.sort() }.zip(pages).filter { it.first != it.second }.map { it.first }.sumOf { it[it.size / 2] }
+        // more readable
+        //        return pages
+        //            .filterNot { it.valid() }
+        //            .map { it.sort() }
+        //            .sumOf { it[it.size / 2] }
     }
 
     private fun List<Int>.valid(): Boolean = sort() == this