[PTA刷题]一元多项式的乘法与加法运算

设计函数分别求两个一元多项式的乘积与和。

输入格式:

输入分2行，每行分别先给出多项式非零项的个数，再以指数递降方式输入一个多项式非零项系数和指数（绝对值均为不超过1000的整数）。数字间以空格分隔。

输出格式:

输出分2行，分别以指数递降方式输出乘积多项式以及和多项式非零项的系数和指数。数字间以空格分隔，但结尾不能有多余空格。零多项式应输出

0
0

。

输入样例:

4 3 4 -5 2  6 1  -2 0
3 5 20  -7 4  3 1

输出样例:

15 24 -25 22 30 21 -10 20 -21 8 35 6 -33 5 14 4 -15 3 18 2 -6 1
5 20 -4 4 -5 2 9 1 -2 0

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

typedef struct PolyNode *Polynomial;
struct PolyNode{
int coef;
int expo;
Polynomial next;
};

Polynomial read();
Polynomial add(Polynomial P1, Polynomial P2);
Polynomial multi(Polynomial P1, Polynomial P2);
void print(Polynomial P);
void attach(int coef, int expo, Polynomial *rear);

int main(){
Polynomial P1=read();
Polynomial P2=read();
Polynomial P3=add(P1, P2);
Polynomial P4=multi(P1, P2);
print(P4);
print(P3);
return 0;
}

Polynomial
4000
read()
{
Polynomial P = (Polynomial)malloc(sizeof(struct PolyNode));
P->next=NULL;
Polynomial rear,temp;
rear=P;
int num, pcoef, pexpo;
scanf("%d", &num);

while (num) {
scanf("%d %d", &pcoef, &pexpo);
attach(pcoef,pexpo,&rear);
num--;
}
temp=P; P=P->next; free(temp);
return P;

}

void attach(int coef, int expo, Polynomial *rear)
{
Polynomial temp = (Polynomial)malloc(sizeof(struct PolyNode));
temp->next=NULL;
temp->coef=coef;
temp->expo=expo;
(*rear)->next=temp;
*rear=temp;
}

void print(Polynomial P)
{
if(!P){
printf("0 0\n"); return;
}
while (P) {
if(P->next){
printf("%d %d ",P->coef,P->expo);
}
else
printf("%d %d",P->coef,P->expo);
P=P->next;
}
printf("\n");
}

Polynomial add(Polynomial P1, Polynomial P2)
{
Polynomial P,rear,temp2,t1,t2;
P=(Polynomial)malloc(sizeof(struct PolyNode));
P->next=NULL;
rear=P;
t1=P1;t2=P2;

while (t1 && t2) {
if(t1->expo > t2->expo){ //看下面的注释
attach(t1->coef, t1->expo, &rear);
t1=t1->next;
}
else if(t1->expo < t2->expo){
attach(t2->coef, t2->expo, &rear);
t2=t2->next;
}
else{
int tempcoef=t1->coef + t2->coef;
if(tempcoef){
attach(tempcoef, t1->expo, &rear);
}
t1=t1->next;
t2=t2->next;
}
}
while(t1){
attach(t1->coef, t1->expo, &rear);
t1=t1->next;
}

while(t2){
attach(t2->coef, t2->expo, &rear);
t2=t2->next;
}

temp2=P;
P=P->next; free(temp2);

return P;
}

Polynomial multi(Polynomial P1, Polynomial P2)
{
Polynomial P,rear,t1,t2,t;
int c,e;
if(!P1 || !P2) return NULL;

P=(Polynomial)malloc(sizeof(struct PolyNode));
P->next=NULL;
rear=P;
t1=P1;t2=P2;

while(t2){
attach(t1->coef*t2->coef, t1->expo+t2->expo, &rear);

t2=t2->next;
}

t1=t1->next;
while(t1){
t2=P2;rear=P;
while(t2){
c=t1->coef*t2->coef;
e=t1->expo+t2->expo;

while (rear->next && rear->next->expo>e) {
rear=rear->next;
}
if(rear->next && rear->next->expo ==e){
if(rear->next->coef+c){
rear->next->coef+=c;
}
else{
t=rear->next;
rear->next=t->next;
free(t);
}
}
else{
t=(Polynomial)malloc(sizeof(struct PolyNode));
t->coef=c;t->expo=e;
t->next=rear->next;
rear->next=t;
rear=rear->next;
}

t2=t2->next;
}
t1=t1->next;
}
t2=P; P=P->next; free(t2);

return P;
}

一开始写的时候，add函数写错了，会改变原来的P1和P2。

我写的：

rear->next = t1; //!!!

t1 = t1->next;

rear = rear->next;

怎么可以把rear直接指到原来的链表的结点上去呢……

这样子对rear进行操作，就会改变原来的链表结构了。

总之，好好学指针啊！

而且最后程序好像还是有问题……输出0 0有问题。