#!/bin/bash
#
# ex1.bash: Advent2020 game, day 9/game 1.

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
}
[[ $# = 1 ]] && N=$1

push
declare -i i target
for ((i=N; i<SIZE; ++i)); do
	badnum $i || break
done
target="${LIST[$i]}"

printf "%s : res=%d\n" "$CMD" "$target"

exit 0