palindrome_permutation.rb

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