说明：  一份很完美的哈夫曼编码译码器得实习报告。源程序功能有编码，译码，打印哈夫曼树。是数据结构实习课得一个范例。
(A very perfect Huffman decoder have internship report. Source function has encoding, decoding, printing Huffman tree. Data structure is an example of a practical lesson.)