From eb3803e9429a6701cf13c535bbcca9c836357dd2 Mon Sep 17 00:00:00 2001
From: Matej Focko <mfocko@redhat.com>
Date: Mon, 6 Dec 2021 11:15:39 +0100
Subject: [PATCH] day(06): do not recreate list every time

Signed-off-by: Matej Focko <mfocko@redhat.com>
---
 src/day06/Day06.kt | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/src/day06/Day06.kt b/src/day06/Day06.kt
index f258670..83c5dd2 100644
--- a/src/day06/Day06.kt
+++ b/src/day06/Day06.kt
@@ -3,14 +3,10 @@ package day06
 import readInputAsCommaSeparatedInts
 
 fun howManyAfter(input: List<Int>, days: Int): Long =
-    (1..days)
-        .fold(List(9) { i -> input.count { it == i }.toLong() }) { counts, _ ->
-            List(9) { i ->
-                when (i) {
-                    6 -> counts[0] + counts[7]
-                    else -> counts[(i + 1) % 9]
-                }
-            }
+    (0 until days)
+        .fold(MutableList(9) { i -> input.count { it == i }.toLong() }) { counts, day ->
+            counts[(7 + day) % 9] += counts[day % 9]
+            counts
         }
         .sum()