对简单的一元多项式相加、相减运算

一元多项式相加、相减运算可以使用上面的链表实现。假设有两个多项式 $p_1$ 和 $p_2$，它们的单项式按照指数从大到小排列，可以按照以下方式实现相加、相减运算：

def add(p1, p2):
    result = Polynomial()
    current_p1 = p1.head.next
    current_p2 = p2.head.next
    while current_p1 is not None and current_p2 is not None:
        if current_p1.exp == current_p2.exp:
            result.insert(current_p1.coef + current_p2.coef, current_p1.exp)
            current_p1 = current_p1.next
            current_p2 = current_p2.next
        elif current_p1.exp > current_p2.exp:
            result.insert(current_p1.coef, current_p1.exp)
            current_p1 = current_p1.next
        else:
            result.insert(current_p2.coef, current_p2.exp)
            current_p2 = current_p2.next
    while current_p1 is not None:
        result.insert(current_p1.coef, current_p1.exp)
        current_p1 = current_p1.next
    while current_p2 is not None:
        result.insert(current_p2.coef, current_p2.exp)
        current_p2 = current_p2.next
    return result

def sub(p1, p2):
    result = Polynomial()
    current_p1 = p1.head.next
    current_p2 = p2.head.next
    while current_p1 is not None and current_p2 is not None:
        if current_p1.exp == current_p2.exp:
            result.insert(current_p1.coef - current_p2.coef, current_p1.exp)
            current_p1 = current_p1.next
            current_p2 = current_p2.next
        elif current_p1.exp > current_p2.exp:
            result.insert(current_p1.coef, current_p1.exp)
            current_p1 = current_p1.next
        else:
            result.insert(-current_p2.coef, current_p2.exp)
            current_p2 = current_p2.next
    while current_p1 is not None:
        result.insert(current_p1.coef, current_p1.exp)
        current_p1 = current_p1.next
    while current_p2 is not None:
        result.insert(-current_p2.coef, current_p2.exp)
        current_p2 = current_p2.next
    return result

以上代码中，`add` 函数和 `sub` 函数分别实现了多项式的加法和减法，返回一个新的多项式。在循环中，比较两个多项式当前单项式的指数大小，如果相同则将系数相加（或相减），否则插入指数较大的单项式。最后，如果有一个多项式已经遍历完，则将另一个多项式的剩余单项式全部插入到结果多项式中。

使用示例：

p1 = Polynomial()  # 2x^3+3x^2-4x+1
p1.insert(2, 3)
p1.insert(3, 2)
p1.insert(-4, 1)
p1.insert(1, 0)

p2 = Polynomial()  # -x^2+2x+1
p2.insert(-1, 2)
p2.insert(2, 1)
p2.insert(1, 0)

p3 = add(p1, p2)  # 2x^3+2x^2-2x+2
print(p3)  # 2x^3+2x^2-2x+2

p4 = sub(p1, p2)  # 2x^3+4x^2-6x
print(p4)  # 2x^3+4x^2-6x