设计一个多项式类，支持多项式的显示、加减运算、相乘运算，并且必须 使用链式结构来实现该多项式类，包括多项式的存储、显示与运算等等。-Design a polynomial class, support the display of the polynomial, subtraction, multiplication by chain structure and must be used to achieve the polynomial class, including the polyn