#!/bin/sh

read dummy
read -a ARRAY
FILTER=()

# X (listof X) -> Boolean
member () {
  for i in ${@:2}; do
    if [[ $1 -eq $i ]]; then
        return 0
    fi
  done
  return 1
}

# X (listof X) -> (listof X)
filter () {
  new=()
  for i in ${@:2}; do
    if ! [[ $i -eq $1 ]]; then
        new+=($i)
    fi
  done
  # bash functions don't return values, so we use global vars instead
  FILTER=${new[@]}
}

# (listof X) -> X
lonelyint () {
  # () to properly create an array from element
  array=("$@")
  count=0

  for current in ${array[@]}; do
    let 'count++'
    rest=${array[@]:$count}
    if member $current $rest; then
        # this filter doesn't really work
        # array=(2 32 2) current=2 => array=(3)
        #new=${array[@]/$current/}
        filter $current ${array[@]}
        lonelyint ${FILTER[@]}
    else
        echo "$current"
        exit 0
    fi
  done
}

lonelyint ${ARRAY[@]}