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

需要设置一个变量存储进位，考察链表的操作(遍历，初始化)

/**
 * 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 * ptr = NULL;
        ListNode * next = NULL;
        bool carry = false;
        int val;
        while(l1!=NULL || l2!=NULL){
            val = 0;
            if(l1!=NULL){
                val = val+l1->val;
                l1 = l1->next;
            }
            if(l2!=NULL){
                val = val+l2->val;
                l2 = l2->next;
            }
            if(carry == true){
                val = val+1;
                carry = false;
            }
            ListNode * temp = new ListNode(val%10);
            carry = val/10;
            if(ptr == NULL){
                ptr = temp;
                next = ptr;
            }
            else{
                next->next = temp;
                next = temp;
            }
        }
        if(carry){
            next->next = new ListNode(1);
        }
        return ptr;
    }
};