2-1 Add Two Polynomials (20 分)

Write a function to add two polynomials. Do not destroy the input. Use a linked list implementation with a dummy head node. Note: The zero polynomial is represented by an empty list with only the dummy head node.

Format of functions:

Polynomial Add( Polynomial a, Polynomial b );

where Polynomial is defined as the following:

typedef struct Node *PtrToNode;
struct Node {
    int Coefficient;
    int Exponent;
    PtrToNode Next;
};
typedef PtrToNode Polynomial;
/* Nodes are sorted in decreasing order of exponents.*/

The function Add is supposed to return a polynomial which is the sum of a and b.

Sample program of judge:

#include <stdio.h>
#include <stdlib.h>
typedef struct Node *PtrToNode;
struct Node  {
    int Coefficient;
    int Exponent;
    PtrToNode Next;
};
typedef PtrToNode Polynomial;

Polynomial Read(); /* details omitted */
void Print( Polynomial p ); /* details omitted */
Polynomial Add( Polynomial a, Polynomial b );

int main()
{
    Polynomial a, b, s;
    a = Read();
    b = Read();
    s = Add(a, b);
    Print(s);
    return 0;
}

/* Your function will be put here */

Sample Input:

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

Sample Output:

5 20 -4 4 -5 2 9 1 -2 0

1.系数为0要跳过

2.上来给你个空表，反手就把另一个返回去

3.记住链表头结点是空的，第二个才存数据

Polynomial Add( Polynomial a, Polynomial b ){
    if(a == NULL) return b;
    if(b == NULL) return a;
    Polynomial ans, tmp, before; //ans是头结点, before指向tmp前一个结点
    before = (Polynomial)malloc(sizeof(Polynomial));
    ans = before;
    a = a->Next;
    b = b->Next;
    while(a != NULL && b != NULL){
        tmp = (Polynomial)malloc(sizeof(Polynomial));
        before->Next = tmp;
        if(a->Exponent == b->Exponent){
            tmp->Exponent = a->Exponent;
            tmp->Coefficient = a->Coefficient + b->Coefficient;
            a = a->Next;
            b = b->Next;
            if(tmp->Coefficient == 0)continue;//0不存
        }
        else if(a->Exponent > b->Exponent){
            tmp->Exponent = a->Exponent;
            tmp->Coefficient = a->Coefficient;
            a = a->Next;
        }
        else{
            tmp->Exponent = b->Exponent;
            tmp->Coefficient = b->Coefficient;
            b = b->Next;
        }
        before = tmp;
    }
    if(a != NULL) before->Next = a;//后面全接上剩下的部分
    else before->Next = b;// 
    return ans;
}