将两个多项式相加

题目链接：https://pintia.cn/problem-sets/434/problems/5803

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

typedef struct PolyNode* PtrToPolyNode;
struct PolyNode {
    int Coef;
    int Expon;
    PtrToPolyNode Next;
};

typedef struct PolyNode* Polynomial;


int Compare(int e1, int e2)
{    //比较两项指数e1和e2，根据大、小、等三种情况分别返回1， -1， 0
    if (e1 > e2)
        return 1;
    else if (e1 < e2)
        return -1;
    else
        return 0;
}

void Attach(int coef, int expon, Polynomial *PtrRear)
{
    Polynomial p = (Polynomial)malloc(sizeof(struct PolyNode));
    p -> Coef = coef;
    p->Expon = expon;
    p->Next = NULL;
    (*PtrRear)->Next = p;
    *PtrRear = p;
}

Polynomial PolyAdd(Polynomial P1, Polynomial P2)
{
    Polynomial front, rear, temp;
    int sum;
    front = rear = (Polynomial)malloc(sizeof(struct PolyNode));
    while (P1 && P2)
    {
        switch (Compare(P1->Expon, P2->Expon))
        {
        case 1:
            Attach(P1->Coef, P1->Expon, &rear);
            P1 = P1->Next;
            break;
        case -1:
            Attach(P2->Coef, P2->Expon, &rear);
            P2 = P2->Next;
            break;
        case 0:
            sum = P1->Coef + P2->Coef;
            if (sum)
                Attach(sum, P1->Expon, &rear);
            P1 = P1->Next;
            P2 = P2->Next;
            break;
        }
    }
    while (P1)
    {
        Attach(P1->Coef, P1->Expon, &rear);
        P1 = P1->Next;
    }
    while (P2)
    {
        Attach(P2->Coef, P2->Expon, &rear);
        P2 = P2->Next;
    }
    rear->Next = NULL;
    temp = front;
    front = front->Next;
    free(temp);
    return front;
}

Polynomial CreatePoly()
{
    int n, coef, expon;
    Polynomial front, rear, temp;
    
    front = rear = (Polynomial)malloc(sizeof(struct PolyNode));
    scanf_s("%d", &n);
    while (n--)
    {
        scanf_s("%d %d", &coef, &expon);
        Attach(coef, expon, &rear);
    }
    rear->Next = NULL;
    temp = front;
    front = front->Next;
    free(temp);
    return front;
}

void printPoly(Polynomial P)
{
    Polynomial cell;
    cell = P;
    for (cell; cell; cell = cell->Next)
    {
        printf("%dX^%d ", cell->Coef, cell->Expon);
    }
}

int main()
{
    Polynomial P1, P2, P3;
    P1 = CreatePoly();
    P2 = CreatePoly();
    P3 = PolyAdd(P1, P2);
    printPoly(P3);

}