LeetCode_2. Add Two Numbers.cpp

/**
 * 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) {
        vector<int> sum;
        int i;
        int hold = 0;
        for (i = 0; (l1 != NULL) || (l2 != NULL); i++)
        {
            sum.push_back(hold);
            if (l1 != NULL)
            {
                sum[i] += l1->val;
                l1 = l1->next;
            }
            if (l2 != NULL)
            {
                sum[i] += l2->val;
                l2 = l2->next;
            }
            hold = (int)sum[i] / 10;
            if(hold)
                sum[i] %= 10;
        }
        if(hold)
            sum.push_back(hold);

        ListNode *root = new ListNode(0);
        ListNode *ptr;
        ptr = root;
        for (i = 0; i < sum.size(); i++)
        {
            ptr->next = new ListNode(sum[i]);
            ptr = ptr->next;
        }
        ptr = root->next;
        delete root;
        return ptr;
    }
};L

sum.push_back(hold); // line17 run time error when use sum[i] = hold;