利用哈夫曼编码进行通信可以大大提高信道利用率，缩短信息传输时间，降低传输成本。但是，这要求在发送端通过一个编码系统对待传数据预先编码，在接收端将传来的数据进行译码。对于双工信道（即可以双向传输信息的信道），每端都需要一个完整的编码或译码系统。试为这样的信息发送站写一个哈夫曼码的编码系统。(Using Huffman coding for communication can greatly improve the channel utilization, shorten the transmission time and reduce the transmission cost. However, it is required that the transmitted data be encoded by a coding system at the sending end and decoded by the receiver. For a duplex channel (i.e., a channel capable of two-way transmission of information), each end requires a complete encoding or decoding system. Write a Huffman code system for this information sending station.)