说明：  (1)建立含有若干个元素的带表头的单链表； 要求从键盘输入和文件读入两个多项式，显示并保存。 （2）设有一元多项式Am(x)和Bn(x). Am(x)=A0+A1x1+A2x2+A3x3+...+Amxm Bn(x)=B0+B1x1+B2x2+B3x3+...+Bnxn 请实现求M(x)=Am(x)+Bn(x)、M(x)=Am(x)-Bn(x)、M(x)=Am(x)×Bn(x)以及计算M(x)=0的根，计算多项式在x处的值，求多项式M的导函数M，并将结果保存在文本文件中。 （3）多项式的输出形式为类数学表达式。例如，多项式-3x8+6x3-18的输出形式为-3x^8+6x^3-18，x15+(-8)x7-14的输出形式为x^15+8x^7-14。注意，数值为1的非零次项的输出形式中略去系数1，如项1x8的输出形式为x8，项-1x3的输出形式为-x3。
((1)A single linked list with a number of elements is set up. Requirements from keyboard input and file read two polynomials, display and save. (2) there are one polynomial Am (x) and Bn (x). Am (x) =A0+A1x1+A2x2+A3x3+... +Amxm Bn (x) =B0+B1x1+B2x2+B3x3+... +Bnxn M (x) =Am (x) +Bn (x), M (x) =Am (x) -Bn (x), M (x), and calculated polynomials are calculated, and the derivative of polynomial is calculated and the results are saved in the text file. (3) the output form of polynomials is a class of mathematical expressions. For example, the output form of polynomial -3x8+6x3-18 is -3x^8+6x^3-18, and the output form of x15+ (-8) x7-14 is x^15+8x^7-14. Note that the coefficient of 1 in the output form of the nonzero term with a value of 1 is equal to 1, for example, the output form of item 1x8 is X8, and the output form of item -1x3 is -x3.)