rename repo, subdir for yearly challenges

2020/day09/ex2.bash

@@ -0,0 +1,75 @@
+#!/bin/bash
+#
+# ex1.bash: Advent2020 game, day 9/game 2.
+
+CMD=${0##*/}
+shopt -s extglob
+
+declare -i N=5 SIZE
+declare -a LIST=()
+
+function push25 () {
+	local i
+	for ((i=0; i<25; ++i)); do
+		read -r i
+		LIST+=("$i")
+	done
+}
+
+function push() {
+	local i
+	while read -r i; do
+		LIST+=("$i")
+	done
+	SIZE=${#LIST[@]}
+}
+
+function badnum() {
+	local -i cur="$1" i j
+	local -i res=${LIST[$cur]}
+	local -i start=$((cur-N-1))
+	for ((i=start; i<cur; ++i)); do
+		for ((j=i+1; j<cur; ++j)); do
+			if (((LIST[i]+LIST[j]) == res)); then
+				return 0
+			fi
+		done
+	done
+	return 1
+}
+
+function findsum() {
+	local -i target=$1 start=$2 i
+	local -i sum=0
+	local -i small=${LIST[$start]}
+	local -i high=$small
+
+	for ((i=start; i<SIZE && sum<target; ++i)); do
+		((cur=${LIST[$i]}))
+		((sum+=cur))
+		((cur<small)) && small=$cur
+		((cur>high)) && high=$cur
+
+		if ((sum==target)); then
+			echo $((small+high))
+			return 0
+		fi
+	done
+	return 1
+}
+
+
+[[ $# = 1 ]] && N=$1
+
+push
+declare -i i target num
+for ((i=N; i<SIZE; ++i)); do
+	badnum $i || break
+done
+target="${LIST[$i]}"
+for ((i=0; i<SIZE; ++i)); do
+	num=$(findsum "$target" $i) && break
+done
+printf "%s : res=%d sum=%d\n" "$CMD" "$target" "$num"
+
+exit 0