added my 1st (slow on exercise 2) bash version.

day15/ex1-2-slow.bash

@@ -0,0 +1,65 @@
+#!/bin/bash
+#
+# ex1.bash: Advent2020 game, day 15/games 1 and 2.
+# ===> Too slow for exercise 2, needed to rewrite the algorithm.
+
+CMD=${0##*/}
+#shopt -s extglob
+
+declare -A prev nums
+declare -i cur=0 last
+
+
+function print_binary() {
+	local -i num=$1 exp
+	local str="" format="%0${2}d"
+
+	for ((exp=1; num>exp; exp<<=1)); do
+		if ((num & exp)); then
+			str=1"$str"
+		else
+			str=0"$str"
+		fi
+		 echo " str=$str"
+	done
+	printf "$format" $str
+}
+
+function print_array() {
+	local -i i
+
+	printf "last: %d\n" "$last"
+	printf "nums:\n"
+	for i in "${!nums[@]}"; do
+		printf "  %6d => %d\n" "$i" "${nums[$i]}" >&2
+		if [[ -v prev[$i] ]]; then
+			printf "        prev => %d\n" "${prev[$i]}" >&2
+		fi
+	done
+}
+
+TARGET=$1
+IFS=","
+read -r line
+set -- $line
+while (($# > 0)); do
+	nums[$1]=$cur
+	last=$1
+	((cur++))
+	shift
+done
+
+for ((; cur != TARGET; ++cur)); do
+	diff=0
+	if [[ -v prev[$last] ]]; then
+		((diff=nums[$last]-prev[$last]))
+		prev[$last]=${nums[$last]}
+	fi
+	[[ -v nums[$diff] ]] && prev[$diff]=${nums[$diff]}
+	nums[$diff]=$cur
+	last=$diff
+done
+
+printf "%s : res=%d\n" "$CMD" "$last"
+
+exit 0

day15/ex1.bash

@@ -1,6 +1,6 @@
 #!/bin/bash
 #
-# ex1.bash: Advent2020 game, day 15/game 1.
+# ex1.bash: Advent2020 game, day 15/games 1 and 2.
 
 CMD=${0##*/}
 #shopt -s extglob