3-1 一元多项式求导

标准解答：

#include <stdio.h>
#include <stdlib.h>

typedef struct PolyNode *Polynomial;
struct PolyNode {
    int coef;
    int expon;
    Polynomial Next;
};
void Attach(int c, int e, Polynomial *pRear)
{
    Polynomial P;
    P = (Polynomial)malloc(sizeof(struct PolyNode));    //申请一个新结点
    P->coef = c;    //对新结点赋值
    P->expon = e;
    P->Next = NULL;
    (*pRear)->Next = P;
    *pRear = P;
}

Polynomial ReadPoly()
{
    //读入并建立多项式
    Polynomial P, Rear, t;
    int c, e;
    //为了程序处理方便起见，先构造一个链表空节点
    P = (Polynomial)malloc(sizeof(struct PolyNode));
    Rear = P;
    while (scanf_s("%d %d", &c, &e) != EOF)
        Attach(c, e, &Rear);

    //删除头结点
    t = P;
    P = P->Next;
    free(t);
    return P;
}

Polynomial PolyDifferentiation(Polynomial P)
{
    //求多项式的导数函数，返回结果多项式
    Polynomial P1, P2;
    P2 = P, P1 = NULL;        //P1总指向p2的前一项
    while (P2 && P2->expon)
    {
        P2->coef = P2->coef * P2->expon;
        P2->expon--;
        P1 = P2;
        P2 = P2->Next;
    }
    if (P2)        //如果多项式中存在常数项
    {
        if (P1) {            //如果常数项不是第一项，也就是P1 != NULL
            free(P2);
            P1->Next = NULL;
        }
        else        //P1 = NULL, 也就是说常数项是第一项
        {
            P2->coef = 0;
        }
    }
    return P;
}

void PrintPoly(Polynomial P)
{
    //输出多项式
    int flag = 0;
    while (P)
    {
        if (!flag)
            flag = 1;
        else
            printf(" ");
        printf("%d %d", P->coef, P->expon);
        P = P->Next;
    }
    printf("
");
}

int main()
{
    Polynomial P;
    P = ReadPoly();
    P = PolyDifferentiation(P);            //求导函数
    PrintPoly(P);    //输出多项式

    return 0;
}

粗糙解答：

int main()
{
    int coef, expon;
    Polynomial front, rear, temp;
    front = rear = (Polynomial)malloc(sizeof(struct PolyNode));
    while (scanf_s("%d %d", &coef, &expon) != EOF)
    {
        temp = (Polynomial)malloc(sizeof(struct PolyNode));
        temp -> coef = coef * expon;
        temp -> expon = expon -1;
        temp ->Next = NULL;
        rear->Next = temp;
        rear = temp;
    }
    if (front->Next->expon == -1)　　　　//如果常数项是第一项
        printf("0 0
");
    else
    {
        for (temp = front->Next; temp->Next; temp = temp->Next)
            printf("%d %d ", temp->coef, temp->expon);
        if (temp->expon != -1)
            printf("%d %d
", temp->coef, temp->expon);　　　　//并没有将（0， -1）的结点删去，只是没有输出而已
    }    
    return 0;
}