写一个一元稀疏多项式计算的C++源代码，利用链表实现加法减法的计算

好的，这是一份简单的一元稀疏多项式计算的C++源代码，利用链表实现加法减法的计算：

#include <iostream>
using namespace std;

// 多项式项
class PolyItem {
public:
    int coef;  // 系数
    int expn;  // 指数
    PolyItem* next;  // 下一个项
};

// 多项式
class Poly {
public:
    Poly() {
        head = new PolyItem();
        head->next = nullptr;
    }
    ~Poly() {
        PolyItem* p = head;
        while (p) {
            PolyItem* temp = p;
            p = p->next;
            delete temp;
        }
    }

    // 获取多项式项的个数
    int GetLength() const {
        int count = 0;
        PolyItem* p = head->next;
        while (p) {
            count++;
            p = p->next;
        }
        return count;
    }

    // 添加多项式项
    void AddItem(int coef, int expn) {
        PolyItem* p = head;
        while (p->next && p->next->expn > expn) {
            p = p->next;
        }
        if (p->next && p->next->expn == expn) {
            // 合并同类项
            p->next->coef += coef;
            if (p->next->coef == 0) {
                // 系数为0，删除该项
                PolyItem* temp = p->next;
                p->next = p->next->next;
                delete temp;
            }
        } else {
            PolyItem* item = new PolyItem();
            item->coef = coef;
            item->expn = expn;
            item->next = p->next;
            p->next = item;
        }
    }

    // 加法运算
    void Add(const Poly& b) {
        PolyItem* pa = head->next;
        PolyItem* pb = b.head->next;
        PolyItem* pc = head;

        while (pa && pb) {
            if (pa->expn > pb->expn) {
                pc->next = new PolyItem();
                pc = pc->next;
                pc->coef = pa->coef;
                pc->expn = pa->expn;
                pa = pa->next;
            } else if (pa->expn < pb->expn) {
                pc->next = new PolyItem();
                pc = pc->next;
                pc->coef = pb->coef;
                pc->expn = pb->expn;
                pb = pb->next;
            } else {
                int sum = pa->coef + pb->coef;
                if (sum != 0) {
                    pc->next = new PolyItem();
                    pc = pc->next;
                    pc->coef = sum;
                    pc->expn = pa->expn;
                }
                pa = pa->next;
                pb = pb->next;
            }
        }

        while (pa) {
            pc->next = new PolyItem();
            pc = pc->next;
            pc->coef = pa->coef;
            pc->expn = pa->expn;
            pa = pa->next;
        }

        while (pb) {
            pc->next = new PolyItem();
            pc = pc->next;
            pc->coef = pb->coef;
            pc->expn = pb->expn;
            pb = pb->next;
        }

        pc->next = nullptr;
    }

    // 减法运算
    void Subtract(const Poly& b) {
        PolyItem* pa = head->next;
        PolyItem* pb = b.head->next;
        PolyItem* pc = head;

        while (pa && pb) {
            if (pa->expn > pb->expn) {
                pc->next = new PolyItem();
                pc = pc->next;
                pc->coef = pa->coef;
                pc->expn = pa->expn;
                pa = pa->next;
            } else if (pa->expn < pb->expn) {
                pc->next = new PolyItem();
                pc = pc->next;
                pc->coef = -pb->coef;
                pc->expn = pb->expn;
                pb = pb->next;
            } else {
                int diff = pa->coef - pb->coef;
                if (diff != 0) {
                    pc->next = new PolyItem();
                    pc = pc->next;
                    pc->coef = diff;
                    pc->expn = pa->expn;
                }
                pa = pa->next;
                pb = pb->next;
            }
        }

        while (pa) {
            pc->next = new PolyItem();
            pc = pc->next;
            pc->coef = pa->coef;
            pc->expn = pa->expn;
            pa = pa->next;
        }

        while (pb) {
            pc->next = new PolyItem();
            pc = pc->next;
            pc->coef = -pb->coef;
            pc->expn = pb->expn;
            pb = pb->next;
        }

        pc->next = nullptr;
    }

    // 显示多项式
    void Display() const {
        PolyItem* p = head->next;
        while (p) {
            cout << p->coef << "x^" << p->expn;
            if (p->next) {
                cout << " + ";
            }
            p = p->next;
        }
        cout << endl;
    }

private:
    PolyItem* head;
};

int main() {
    Poly a, b, c;

    // 添加多项式项
    a.AddItem(3, 2);
    a.AddItem(4, 1);
    a.AddItem(5, 0);
    b.AddItem(1, 2);
    b.AddItem(-3, 1);
    b.AddItem(2, 0);

    // 显示多项式
    cout << "a = ";
    a.Display();
    cout << "b = ";
    b.Display();

    // 加法运算
    c = a;
    c.Add(b);
    cout << "a + b = ";
    c.Display();

    // 减法运算
    c = a;
    c.Subtract(b);
    cout << "a - b = ";
    c.Display();

    return 0;
}

在这个源代码中，我们定义了两个类：PolyItem和Poly。PolyItem表示多项式的一项，包括系数和指数。Poly表示多项式，包括多项式项的链表和一些操作，如添加多项式项、加法运算、减法运算和显示多项式。我们可以创建两个多项式a和b，添加多项式项，然后进行加法和减法运算。最后，我们可以显示结果多项式c。