From 11d744f1cd2c87d7dc01c504e368d4cecd99aa47 Mon Sep 17 00:00:00 2001
From: Brett Parker <iDunno@sommitrealweird.co.uk>
Date: Tue, 15 Dec 2020 16:30:20 +0000
Subject: [PATCH] Use a variable reference for where to store the result, stop
 putting all results in to a huge array and then reading the answer from that.
 Save a fair chunk of memory.

---
 day15/memory.sh | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/day15/memory.sh b/day15/memory.sh
index 4f16b3b..a2d9547 100755
--- a/day15/memory.sh
+++ b/day15/memory.sh
@@ -12,10 +12,11 @@ read_file() {
 get_answer() {
     local number=$1
     local count=$2
+    local -n __fn_result=$3
     if [ ${lastseen[$number]+a} ]; then
-        answers[$count]=$((count-${lastseen[$number]}-1))
+        __fn_result=$((count-${lastseen[$number]}))
     else
-        answers[$count]=0
+        __fn_result=0
     fi
 }
 
@@ -39,40 +40,40 @@ filename="${1:-p1_436.txt}"
 read_file "$filename"
 
 declare -A lastseen
-declare -a answers
 
 current_answer=-1
 last_answer=-1
 count=0
 
+result=
+
 for number in ${data[@]}; do
     count=$((count+1))
     last_answer=$current_answer
     if [ $last_answer -ge 0 ]; then
         lastseen[$last_answer]=$((count-1))
     fi
-    answers[$count]=$number
     current_answer=$number
 done
 
 while [ $count -lt 2020 ]; do
-    count=$((count+1))
-    get_answer $current_answer $count
     last_answer=$current_answer
+    get_answer $current_answer $count result
+    count=$((count+1))
+    current_answer=$result
     lastseen[$last_answer]=$((count-1))
-    current_answer=${answers[$count]}
-    $debug_func "$count: ${answers[$count]}"
+    $debug_func "$count: $current_answer"
 done
 
-echo "Part 1: ${answers[$count]}"
+echo "Part 1: $current_answer"
 
 while [ $count -lt 30000000 ]; do
-    count=$((count+1))
-    get_answer $current_answer $count
     last_answer=$current_answer
+    get_answer $current_answer $count result
+    count=$((count+1))
+    current_answer=$result
     lastseen[$last_answer]=$((count-1))
-    current_answer=${answers[$count]}
-    $debug_func "$count: ${answers[$count]}"
+    $debug_func "$count: $current_answer"
 done
 
-echo "Part 2: ${answers[$count]}"
+echo "Part 2: $current_answer"
-- 
2.39.5