稀疏多项式计算器

通过链表的数据结构，实现：创建多项式、显示多项式、复制多项式、销毁多项式、清空多项式、多项式相加、多项式相减、多项式求值等功能。-Sparse polynomial calculator through the list data structure to achieve: Create polynomials, polynomial display, copy polynomials, polynomial destroyed, empty polynomials, polynomials, polynomial subtraction, polynomial evaluation functions.