1002. A+B for Polynomials (25)

题目链接：http://www.patest.cn/contests/pat-a-practise/1002

题目很简单，求两个多项式相加的结果，一开始ZS用数据结构里的链表去敲，只对两组数据，怎么也找不到错误，后来果断换成数组模拟，一次AC，但还是没想明白链表哪错了！

数组模拟AC代码：

#include <iostream>
#include <iomanip>
#include <cstring>
using namespace std;

int main()
{
    double a[1100],b[1100],va;
    int sum,n,temp;
    while (cin>>n)
    {
          memset(a,0,sizeof(a));
          memset(b,0,sizeof(b));
          sum=n;
          while (n--)
          {
                cin>>temp>>va;
                a[temp]=va;
          }
          cin>>n;
          sum+=n;
          while(n--)
          {
                 cin>>temp>>va;
                 b[temp]=va;
                 if (a[temp]==(-b[temp]))
                 {
                     sum-=2;
                     a[temp]=0;
                 }
                 else
                 {
                     if (a[temp]!=0)
                     sum--;
                     a[temp]+=b[temp];
                 }                 
          }
           cout <<sum;
           for (int i=1000;i>=0;i--)
           if(a[i]!=0)
           cout <<" "<<i<<" "<<fixed<<setprecision(1)<<a[i];    
           cout <<endl;
    }
    return 0;
}    

链表wa代码，哪位大神能帮我看看，不胜感激：

#include <iostream>
#include <cstring>
#include <iomanip>
using namespace std;

struct node
{
       double coef;
       int exp;
       node *next;
};

node *listcreat()
{
     int n;
     cin>>n;
     node *head,*rear,*s;
     double c;
     int e;
     head=(node *)malloc(sizeof(node));
     head->exp=n;
     rear=head;
     while (n--)
     {
           cin>>e>>c;
           s=(node *)malloc(sizeof(node));
           s->exp=e;
           s->coef=c;
           rear->next=s;
           rear=s;
     }
     rear->next=NULL;
     return head;
     
}
node *add(node *x,node *y)
{
     x->exp=x->exp+y->exp;
     node *p,*q,*tail,*temp;
     double sum;
     p=x->next;
     q=y->next;
     tail=x;
     while (p!=NULL&&q!=NULL)
     {
           if (p->exp>q->exp)
           {
               tail->next=p;
               tail=p;
               p=p->next;
           }
           else if (p->exp<q->exp)
           {
                tail->next=q;
                tail=q;
                q=q->next;
           }
           else
           {
               if (p->coef+q->coef==0)
               {
                   temp=p;
                   p=p->next;
                   free(temp);
                   temp=q;
                   q=q->next;
                   free(temp);
                   (x->exp)--;
                   (x->exp)--;
               }
               else
               {
                   sum=p->coef+q->coef;
                   p->coef=sum;
                   tail->next=p;
                   tail=p;
                   p=p->next;
                   temp=q;
                   q=q->next;
                   free(q);
                   (x->exp)--;
               }
           }
     }
     if (p==NULL)
         tail=q;
     else
     tail=p;
     return x;
}
int main()
{
   
          node *a,*b;
    a=(node *)malloc(sizeof(node));
    b=(node *)malloc(sizeof(node));
    a=listcreat();
    b=listcreat();
    a=add(a,b);
    cout<<a->exp;
    if (a->exp==0)
    {
         cout <<endl;
         return 0;
    }
    a=a->next;
    while (a!=NULL)
    {
          cout <<" "<<a->exp<<" ";
          cout<<a->coef;
          a=a->next;
    }
    cout <<endl;//}
    return 0;
}