Huffman编码的关键点是构造一棵Huffman树。其过程是：

　　1.输入各个叶子节点及其频率，对每个节点的lchild, rchild, parent分别赋初值为0；

　　2.选择parent为0，且fre最小的两个节点开始建Huffman树，再修改相应节点的lchild, rchild, parent值，如此重复直到Huffman树建立。

　　3.从叶子到根逆向求每个节点的Huffman编码。

4.解压时，由于Huffman编码是前缀编码，即任一字符的编码都不是另一个字符的编码的前缀，故根据码表我们可以轻松实现解压。-Huffman coding key point is to construct a Huffman tree. The process is:

1 Enter each leaf node and frequency, for each node lchild, rchild, parent were given the initial value is 0

2 Select the parent is 0, and the smallest two nodes fre began to build the Huffman tree, and then modify the corresponding node lchild, rchild, parent values​ ​ , so repeat until the Huffman tree created.

3 reverse request from the leaf to the root of the Huffman code for each node.

4 decompression, because Huffman coding is a prefix code, that any one character encoding to another character encoding is not the prefix, so according to code table we can easily extract.