说明：  霍夫曼编码的码长是变化的，对于出现频率高的信息，编码的长度较短；而对于出现频率低的信息，编码长度较长。这样，处理全部信息的总码长一定小于实际信息的符号长度。
(Huffman coding of the code length is variable, for the high frequency information, coding the length of the shorter and for the low frequency information, code length longer. Thus, all information processing must be less than the total code length information symbol length.)