单链表应用------一元多项式

【问题描述】编写一个程序用单链表存储多项式，并实现两个一元多项式A与B相加的函数。A，B刚开始是升序的，A与B之和按降序排列。例如：
多项式A: 1.2X^0 2.5X^1 3.2X^3 -2.5X^5
多项式B: -1.2X^0 2.5X^1 3.2X^3 2.5X^5 5.4X^10
多项式A与B之和：5.4X^10 6.4X^3 5X^1

【输入形式】任意两个多项式A和B

【输出形式】多项式中某一项的系数与指数，系数保留一位小数。

【样例输入】1.2 0 2.5 1 3.2 3 －2.5 5
－1.2 0 2.5 1 3.2 3 2.5 5 5.4 10
2

【样例输出】6.4 3

【样例说明】 第一个多项式的系数与指数对，以空格隔开
第二个多项式的系数与指数对，以空格隔开
输出第２项的系数与指数，系数与指数间用空格隔开，系数保留一位小数

【评分标准】必须用链表实现。

#include <iostream>
#include <cstdio>
using namespace std;
struct Node
{
    float coef;
    int exp;
    Node *next;
};
class Polynomial
{
public:
    Polynomial();
    Polynomial(const Polynomial &B);
    Polynomial operator+ (Polynomial &B);
    void Printk(int k);
    void Print();
private:
    Node *first;
};
Polynomial :: Polynomial()
{
    Node* r =NULL, * s=NULL;
    first = new Node;
    r=first;
    char c;
    do
    {
        s=new Node;
        scanf("%f%d", &s->coef, &s->exp);
        r->next=s;
        r=s;
        c=getchar();

    }while(c != EOF&& c != '\n');
    r->next=NULL;
}
Polynomial::Polynomial(const Polynomial &B)
{
    first=B.first;
}
Polynomial Polynomial:: operator+(Polynomial &B)
{
    Node *pre =first,*p=pre->next;
    Node *qre=B.first,*q=qre->next;
    while(p && q)
    {
        if(p->exp < q->exp)
        {
            pre=p;
            p=p->next;
        }
        else if(p->exp > q->exp)
        {
            qre->next=q->next;
            q->next=p;
            pre->next=q;
            pre=q;
            q=qre->next;

        }
        else
        {
            p->coef = q->coef+p->coef;
            if(p->coef==0)
            {
                pre->next = p->next;
                delete p;
                p=pre->next;
            }
            else
            {
                pre=p;
                p=p->next;
            }
            qre->next=q->next;
            delete q;
            q=qre->next;
        }
    }
    if(q) pre->next = q;
    return *this;
}
void Polynomial::Print()
{
    Node *p=first->next;
    if(p)
        cout<<p->coef<<"x"<<p->exp;
    p=p->next;
    while(p)
    {
        if(p->coef>0)
            cout<<"+"<<p->coef<<"x"<<p->exp;
        else
            cout<<p->coef<<"x"<<p->exp;
        p=p->next;
    }
}
void Polynomial::Printk(int k)
{
    Node* p=first;
    int cnt = 0;
    while (p&&cnt < k)
    {
        p= p->next;
        cnt++;
    }
    Node* prek=first;
    while(p)
    {
        p=p->next;
        prek = prek->next;
    }
    printf("%.1f %d",prek->coef,prek->exp);
}
int main()
{
    Polynomial A,B;

    //A.Print();B.Print();
    A = A+B;
    //cout<<"½á¹ûÊÇ:";
    //A.Print();
    int k;
    cin>>k;
    A.Printk(k);
    return 0;


}