From 5b0a1d7b53a02c1608f62612821c650229b4bf22 Mon Sep 17 00:00:00 2001
From: Bruno Raoult <braoult@gmail.com>
Date: Fri, 30 Jul 2021 20:07:45 +0200
Subject: [PATCH] remove faulty use of sort command (implement qsort in pure
 bash)

---
 2020/day10/OUTPUT   | 12 +++++-------
 2020/day10/ex1.bash | 26 ++++++++++++++++++++++++--
 2020/day10/ex2.bash | 26 ++++++++++++++++++++++++--
 3 files changed, 53 insertions(+), 11 deletions(-)

diff --git a/2020/day10/OUTPUT b/2020/day10/OUTPUT
index 100a55d..d1f7445 100644
--- a/2020/day10/OUTPUT
+++ b/2020/day10/OUTPUT
@@ -1,18 +1,16 @@
-cc -w    ex1-c.c   -o ex1-c
 ex1.bash : diff1=71 diff2=27 res=1917
-	time: 0:00.01 real, 0.00 user, 0.00 sys
-	context-switch:	1+4, page-faults: 0+331
+	time: 0:00.01 real, 0.01 user, 0.00 sys
+	context-switch:	7+1, page-faults: 0+234
 
 ex1-c : diff1=71 diff2=27 res=1917
 	time: 0:00.00 real, 0.00 user, 0.00 sys
 	context-switch:	0+1, page-faults: 0+73
 
-cc -w    ex2-c.c   -o ex2-c
 ex2.bash : size=99 res=113387824750592
-	time: 0:00.01 real, 0.01 user, 0.00 sys
-	context-switch:	2+4, page-faults: 0+329
+	time: 0:00.02 real, 0.02 user, 0.00 sys
+	context-switch:	10+1, page-faults: 0+236
 
 ex2-c : size=99 res=113387824750592
 	time: 0:00.00 real, 0.00 user, 0.00 sys
-	context-switch:	0+1, page-faults: 0+73
+	context-switch:	0+1, page-faults: 0+74
 
diff --git a/2020/day10/ex1.bash b/2020/day10/ex1.bash
index f1e139b..0382b5b 100755
--- a/2020/day10/ex1.bash
+++ b/2020/day10/ex1.bash
@@ -5,9 +5,31 @@
 CMD=${0##*/}
 shopt -s extglob
 
+# quicksort implementation (ascending)
+qsort() {
+   local pivot i smaller=() larger=()
+   qsort_ret=()
+   (($#==0)) && return 0
+   pivot=$1
+   shift
+   for i; do
+      if (( i < pivot )); then
+         smaller+=( "$i" )
+      else
+         larger+=( "$i" )
+      fi
+   done
+   qsort "${smaller[@]}"
+   smaller=( "${qsort_ret[@]}" )
+   qsort "${larger[@]}"
+   larger=( "${qsort_ret[@]}" )
+   qsort_ret=( "${smaller[@]}" "$pivot" "${larger[@]}" )
+}
+
 declare -a numbers
-readarray -t numbers <<< "$(sort -n)"
-numbers=(0 "${numbers[@]}")
+readarray -t numbers
+qsort "${numbers[@]}"
+numbers=(0 ${qsort_ret[@]})
 size=${#numbers[@]}
 ((last=${numbers[size-1]}+3))
 numbers+=("$last")
diff --git a/2020/day10/ex2.bash b/2020/day10/ex2.bash
index 726d3bc..8f21316 100755
--- a/2020/day10/ex2.bash
+++ b/2020/day10/ex2.bash
@@ -5,9 +5,31 @@
 CMD=${0##*/}
 shopt -s extglob
 
+# quicksort implementation (descending)
+qsort() {
+   local pivot i smaller=() larger=()
+   qsort_ret=()
+   (($#==0)) && return 0
+   pivot=$1
+   shift
+   for i; do
+      if (( i > pivot )); then
+         smaller+=( "$i" )
+      else
+         larger+=( "$i" )
+      fi
+   done
+   qsort "${smaller[@]}"
+   smaller=( "${qsort_ret[@]}" )
+   qsort "${larger[@]}"
+   larger=( "${qsort_ret[@]}" )
+   qsort_ret=( "${smaller[@]}" "$pivot" "${larger[@]}" )
+}
+
 declare -a numbers
-readarray -t numbers <<< "$(sort -nr)"
-numbers+=(0)
+readarray -t numbers
+qsort "${numbers[@]}"
+numbers=(${qsort_ret[@]} 0)
 ((last=numbers[0]+3))
 numbers=("$last" "${numbers[@]}")
 size=${#numbers[@]}