说明：  着先通过 HuffmanTree() 函数构造哈夫曼树，然后在主函数 main()中自底向上开始(也就是从数组序号为零的结点开始)向上层层判断，若在父结点左侧，则置码为 0,若在右侧,则置码为 1。最后输出生成的编码
(The first HuffmanTree () function to construct Huffman tree, and then main () main () the bottom up (that is, the array number zero node) to the upper layers of judgment, if the parent node on the left , The code is 0, if on the right side, then the code is 1. And finally outputs the generated code)