remove_white_spaces.rb

def remove_white_spaces(string)
  if (!string || string.size == 0)
    return
  end

  read_index = 0
  write_index = 0
  
  while (read_index < string.length)
    if (string[read_index] != ' ' && string[read_index] != '\t')
      string[write_index] = string[read_index]
      write_index += 1
    end
    read_index += 1 
  end

  string[0, write_index]
end

data = '    All greek  to    me.    '

p remove_white_spaces(data)

Time: O(n)
Space: O(1)