first_nonrepeated_char_eff.rb

def first_nonrepeated_char_eff( string )
  # Create a Hash with default values of 0
  char_counts = Hash.new( 0 )

  # Get rid of spaces
  chars = string.gsub(" ", "").chars

  # Increment the count the hash table for each character
  chars.each do |char|
    char_counts[char] += 1
  end

  # Find the first character with a count of 1 in the hash table
  chars.each do |char|
    return char if char_counts[char] == 1
  end

  # return nil if all characters were repeats
  nil
end