[leetcode刷题系列]Add Two Numbers

模拟题， 也没什么好说的

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode* ret = 0;
        ListNode* cur = 0;
        int carry = 0;
        while(l1 != NULL || l2 != NULL || carry != 0){
            int a = 0;
            int b = 0;
            if(l1 != NULL){
                a = l1->val;
                l1 = l1->next;
            }
            if(l2 != NULL){
                b = l2->val;
                l2 = l2->next;
            }
            int c = a + b + carry;
            carry = c / 10;
            if(cur == NULL){
                cur = ret = new ListNode(c % 10);
            }else{
                cur->next = new ListNode(c % 10);
                cur = cur->next;
            }
        }
        return ret;
    }
};