LeetCode 2. Add Two Numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Examples:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

程序代码：

/** * Definition for singly-linked list. * struct ListNode { * int val; * struct ListNode *next; * }; */
struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
    struct ListNode *p,*q,*r,*m,*tmp;
    p=l1,q=l2;
    int sum=0,flag = 0;
    r = (struct ListNode*)malloc(sizeof(struct ListNode));
    m=r;
    while(p!=NULL&&q!=NULL)
    {
        tmp = (struct ListNode*)malloc(sizeof(struct ListNode));     
        sum =  p->val + q->val + flag;
        flag=sum>=10?1:0;
        tmp->val = sum%10;
        tmp->next = NULL;
        m->next = tmp;
        m= m->next;
        p=p->next;
        q=q->next;
    }
    while(p!=NULL)
    {
        tmp = (struct ListNode*)malloc(sizeof(struct ListNode));     
        sum =  p->val + flag;
        flag=sum>=10?1:0;
        tmp->val = sum%10;
        tmp->next = NULL;
        m->next = tmp;
        m= m->next;
        p=p->next;
    }    
    while(q!=NULL)
    {
        tmp = (struct ListNode*)malloc(sizeof(struct ListNode));     
        sum =  q->val + flag;
        flag=sum>=10?1:0;
        tmp->val = sum%10;
        tmp->next = NULL;
        m->next = tmp;
        m= m->next;
        q=q->next;
    }
    if(flag)
    {
        tmp = (struct ListNode*)malloc(sizeof(struct ListNode));   
        tmp->val = 1;
        tmp->next = NULL;
        m->next = tmp;
        m=m->next;
    }
    return r->next;
}