该程序的主体分为建树、编码、解码三个大块。

建树又可分为3个子过程：频率统计、创建叶子结点单链表、叶子结点连接成树。

单链表的创建过程：对存在的每个字符建立叶子结点，并按权值递增有序插入单链表，再将字符的叶子指针（其作用将在后文提到）指向该结点。

-The program is divided into the main achievements, encoding, decoding three chunks. Contribution can be divided into three sub-processes: frequency statistics to create a single linked list of leaf nodes, leaf nodes connected into a tree. The creation of a single linked list: the establishment of the existing leaf node for each character, according to the weight increment ordered into a single list, and then leaves the character pointer (whose role will be mentioned later) point to the node.