require 'set'
def palindrome_permutation?(input_string)
# create a set to track characters we've seen
charSet = Set.new
# iterate over each character by spitting into an array
input_string.split('').each do |char|
# remove from set if previously added
if charSet.include? char
charSet.delete(char)
# add to set if not already present in set
else
charSet.add(char)
end
end
# set should have 0 or 1 entry if is a palindrome
charSet.length <= 1
end