day 15, bash version

day15/ex1.bash

@@ -0,0 +1,61 @@
+#!/bin/bash
+#
+# ex1.bash: Advent2020 game, day 15/game 1.
+
+CMD=${0##*/}
+#shopt -s extglob
+
+declare -A prev
+declare -i cur=1 last previous
+
+
+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 "${!prev[@]}"; do
+		printf " prev[%d] => %d\n" "$i" "${prev[$i]}" >&2
+	done
+}
+
+TARGET=$1
+IFS=","
+read -r line
+set -- $line
+while (($# > 0)); do
+	prev[$1]=$cur
+	last=$1
+	((cur++))
+	shift
+done
+
+for ((previous=0; cur <= TARGET; ++cur)); do
+	if ((previous)); then
+		((diff=cur-previous-1))
+	else
+		diff=0
+	fi
+	((previous=prev[$diff]))
+	prev[$diff]=$cur
+	last=$diff
+done
+
+printf "%s : res=%d\n" "$CMD" "$last"
+
+exit 0