@cassidoo's 20220619 interview question

prevFib.sh

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

# return true if input is a perfect square
isPerfectSquare () {
  square_root=$( bc <<< "sqrt ($1)" )
  return $( [ $(( $square_root * $square_root )) == $1 ] )
}


# return true if num is Fibby
isFibby () {
  if isPerfectSquare $plus4 || isPerfectSquare $minus4; then
    return 0
  else
    return 1
  fi
}

# return previous Fibby to passed num
getPrevFibby () {
  x=$( bc <<< "(sqrt($plus4) + 0.5) / 1")
  [ $(( $x * $x )) == $plus4 ] || x=$( bc <<< "(sqrt($minus4) + 0.5) / 1")
  echo "$(( ($x - $NUM) / 2 ))"
}

# check for one and only one param
if [ $# -eq 0 ] || [ -n "$(printf '%s\n' "$1" | sed 's/[0-9]//g')" ]; then
  echo "$(basename "$0"): enter a positive integer"
  exit 1
fi
NUM=$1
plus4=$(( 5 * $NUM * $NUM + 4 ))
minus4=$(( 5 * $NUM * $NUM - 4 ))


if isFibby; then
  echo "fibby"
else
  echo "not fibby"
  exit
fi
echo "prevFibby of $NUM is $( getPrevFibby )"

MONTASIO:~ andrewrich$ ~/Documents/scripts/prevFib.sh 55
fibby
prevFibby of 55 is 34
MONTASIO:~ andrewrich$ ~/Documents/scripts/prevFib.sh 144
fibby
prevFibby of 144 is 89
MONTASIO:~ andrewrich$ ~/Documents/scripts/prevFib.sh 145
not fibby