From 60b77d5d3da9d5b929342cececd7590b0d1a8f93 Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Mon, 6 Dec 2021 18:06:13 -0800
Subject: [PATCH] day 6 part 2 Use rotate_left

---
 2021/src/day6.rs | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/2021/src/day6.rs b/2021/src/day6.rs
index 3e8e985..52a0d6e 100644
--- a/2021/src/day6.rs
+++ b/2021/src/day6.rs
@@ -88,16 +88,10 @@ fn part2(input: &str) -> Result<usize> {
         .into_iter()
         .for_each(|n| counts[n] += 1);
     for _ in 0..256 {
-        let mut tmp = [0; 9];
-        for i in 0..9 {
-            if i == 0 {
-                tmp[6] += counts[0];
-                tmp[8] += counts[0];
-            } else {
-                tmp[i - 1] += counts[i];
-            }
-        }
-        counts = tmp;
+        let ready = counts[0];
+        counts.rotate_left(1);
+        counts[6] += ready;
+        counts[8] = ready;
     }
     Ok(counts.iter().sum())
 }