用单链表实现多项式乘法。创建一个PolyNode类，用来保存单项式的内容。单链表用来储存多项式，为方便以见，储存时以降幂排列，这样有利于操作。在程序中操作单链表都是用迭代器来实现的。

在输入单链表时也要以降幂排列输入，相乘过程中每两个单项式相乘，然后将相乘得到的单项式结果插入到乘积多项式的正确位置。-Single linked list to achieve polynomial multiplication. Create a PolyNode class to store the contents of individual style. Polynomial is used to store a single list for the convenience to view, save power when the dynasties arrangement, it is a good operation. Single list in the program operation is achieved using iterative device. When the input should be spelled out in a single list ordered input power, multiply the process of multiplying each of the two individual style, and then multiply the result by the individual style into the correct position of the product polynomial.