@cassidoo's interview question from October 17, 2022

passDoor.sh

#!/usr/bin/env bash
set -eu -o pipefail

# initialize vars
allDoors=() # array

# check input
ARGC="$#" 
if [[ "$ARGC" -ne 2 ]]; then
	echo "Please enter two parameters: number of doors, and number of passes."
	echo "Example: $(basename $0) 7 3"
	exit 1
fi
for P in $@; do
	re='^[0-9]+$'
	if ! [[ $P =~ $re ]] ; then
	   echo "error: $P is not a number" >&2; exit 1
	fi
done

DOORS=$1 PASSES=$2
# all doors start off closed
for door in $( seq 0 $(($DOORS -1)) ); do
	allDoors+=("1")
done
echo "All doors start out closed: ${allDoors[@]}"

# iterate over doors for each pass
for pass in $( seq 1 $PASSES ); do
	for (( door=$(($pass-1)); door<$DOORS; door+=$pass)); do
		case ${allDoors[$door]} in
			'0')
				allDoors[$door]="1"
				;;
			'1')
				allDoors[$door]="0"
				;;
			*) echo "wat"; exit 1;;
		esac
	done
	echo "After pass $pass: ${allDoors[@]}"
done

MONTASIO:scripts andrewrich$ ./passDoors.sh 7 3
All doors start out closed: 1 1 1 1 1 1 1
After pass 1: 0 0 0 0 0 0 0
After pass 2: 0 1 0 1 0 1 0
After pass 3: 0 1 1 1 0 0 0