两个一元多项式的相乘

//两个一元多项式的相乘

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

struct PolyNode {
    int coefficient;
    int exponent;
    struct PolyNode* next;
};

typedef struct PolyNode*  Polynomial;


//初始化一元链表多项式
Polynomial InitPoly()
{
    Polynomial P, rear, temp;
    P = rear = (Polynomial)malloc(sizeof(struct PolyNode));
    int cnt, coef, expon;        //cnt是多项式的项数 
    printf("Please enter the number of items in the polynomial: ");
    scanf_s("%d", &cnt);
    while (cnt--)
    {
        scanf_s("%d%d", &coef, &expon);
        Polynomial temp = (Polynomial)malloc(sizeof(struct PolyNode));
        temp->coefficient = coef;
        temp->exponent = expon;
        temp->next = NULL;
        rear->next = temp;
        rear = temp;
    }
    temp = P;
    P = P->next;
    free(temp);
    return P;
}

//类似尾插法创建链表
void Attach(int coef, int expon, Polynomial *pRear)
{
    Polynomial P = (Polynomial)malloc(sizeof(struct PolyNode));
    P->coefficient = coef;
    P->exponent = expon;
    P->next = NULL;
    (*pRear)->next = P;
    (*pRear) = P;
}

Polynomial PolyMult(Polynomial P1, Polynomial P2)
{
    Polynomial front, rear, temp;
    int c, e;
    if (!P1 || !P2)
        return NULL;
    struct PolyNode* t1, *t2;
    t1 = P1, t2 = P2;
    front = rear = (Polynomial)malloc(sizeof(struct PolyNode));
    while (t2)
    {
        Attach(t1->coefficient * t2->coefficient,
            t1->exponent + t2->exponent, &rear);
        t2 = t2->next;
    }
    t1 = t1->next;
    while (t1)
    {
        t2 = P2;
        rear = front;
        while (t2)
        {
            e = t1->exponent + t2->exponent;
            c = t1->coefficient + t2->coefficient;
            while (rear->next && rear->next->exponent > e)
                rear = rear -> next;
            if (rear->next && rear->next->exponent == e)
            {
                if (rear->next->coefficient + c)
                    rear->next->coefficient += c;
                else
                {
                    temp = rear ->next;
                    rear -> next = rear->next->next;
                    free(temp);
                }
            }
            else
            {
                temp = (Polynomial)malloc(sizeof(struct PolyNode));
                temp -> coefficient = c;
                temp->exponent = e;
                temp->next = rear->next;
                rear->next= temp;
                rear = rear -> next;
            }
            t2 = t2->next;
        }
        t1 = t1->next;
    }
    temp = front;
    front = front->next;
    free(temp);
    return front;
}

void PrintPoly(Polynomial P)
{
    int flag = 0;        //辅助调整输出格式用
    if (!P)
    {
        printf("0 0
");
        return;
    }
    while (P)
    {
        if (!flag)
            flag = 1;
        else
            printf(" ");
        printf("%dX^%d", P->coefficient, P->exponent);
        P = P -> next;
    }
    printf("
");
        
}



int main()
{
    Polynomial P1 = InitPoly();
    Polynomial P2 = InitPoly();
    PrintPoly(P1);
    PrintPoly(P2);
    Polynomial P3 = PolyMult(P1, P2);
    PrintPoly(P3);

    return 0;
}