LeetCode:Add Two Numbers

You are given two linked lists representing two non-negative numbers. 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.

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

思路：用两个指针pa,pb同时遍历两个链表，如若其中一个指针为空，赋值为0,直到两个指针都为空，遍历结束。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode sum(-1);
        int carry=0;
        ListNode *prev=∑
        ListNode *pa=l1,*pb=l2;
        
        while(pa!=NULL||pb!=NULL)
        {
            const int ai=(pa==NULL?0:pa->val);
            const int bi=(pb==NULL?0:pb->val);
            
            const int value=(ai+bi+carry)%10;
            carry=(ai+bi+carry)/10;
            
            prev->next=new ListNode(value);
            pa=(pa==NULL?NULL:pa->next);
            pb=(pb==NULL?NULL:pb->next);
            prev=prev->next;
            
        }
        
        if(carry>0)
            prev->next=new ListNode(carry);
        return sum.next;
    }
};