remove_duplicates.rb

require 'set'

def remove_duplicates(string)
  hashset = Set.new

  write_index = 0
  read_index = 0

  while (read_index < string.length)
    unless hashset.include?(string[read_index])
      hashset.add(string[read_index])
      
      string[write_index] = string[read_index]
      write_index += 1
    end
    read_index += 1
  end
  string[0, write_index]
end

p remove_duplicates('abbabcddbabcdeedebc')