用单链表表示一元多项式，并实现输入、输出、加、减运算。要求实现： (1)创建多项式 (2)多项式加法 (3)输出多项式 (4)多项式减法

在用单链表表示一元多项式时，我们可以将每个节点设计为存储系数和指数的数据结构。例如，可以创建一个名为`Term`的类，包含两个属性：`coefficient`(系数)和`exponent`(指数)，以及指向下一个项的指针。

以下是关键的步骤和代码实现：

1. **创建多项式(Constructing a Polynomial)**:

class Term:
    def __init__(self, coefficient=0, exponent=0):
        self.coefficient = coefficient
        self.exponent = exponent
        self.next = None

class Polynomial:
    def __init__(self):
        self.head = None

2. **多项式加法/Addition of Polynomials**:

def add_poly(poly1, poly2):
    result = Polynomial()
    current1 = poly1.head
    current2 = poly2.head
    
    while current1 is not None and current2 is not None:
        total_coeff = current1.coefficient + current2.coefficient
        if total_coeff != 0:
            term = Term(total_coeff)
            result.append_term(term)
        if current1.exponent < current2.exponent:
            current1 = current1.next
        else:
            current2 = current2.next
            
    # 处理剩余的部分
    while current1 is not None or current2 is not None:
        if current1 is not None:
            result.append_term(current1)
            current1 = current1.next
        if current2 is not None:
            result.append_term(current2)
            current2 = current2.next
            
    return result

# append_term 函数用于向结果添加新的term

3. **输出多项式/Output Polynomial**:

def print_poly(poly):
    current = poly.head
    while current is not None:
        print(f"{current.coefficient}x^{{{current.exponent}}}", end=" + " if current.next else "\n")
        current = current.next

# 示例：print_poly(result)

4. **多项式减法/Subtraction of Polynomials**:

def subtract_poly(poly1, poly2):
    difference = Polynomial()
    
    for term in poly1:
        temp = Term(-term.coefficient)  # 初始化负值系数
        diff_result = add_poly(temp, poly2)  # 将负值项与原多项式相加得到差值
        difference.append_poly(diff_result)

    return difference

注意：以上代码是基于Python编写的简略示例，实际项目中可能会有错误检查和优化。对于具体的输入输出，你需要处理用户输入转换成`Term`对象的过程。