[leetcode] 2. 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

这道题是计算用链表表示的两个数字之和，题目难度为Medium。

题目比较简单，注意进位的处理即可，就不详细说明了，代码中没有释放内存，具体项目时相信大家都会注意。具体代码：

class Solution {public:    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {        int carry = 0;        ListNode* head = NULL;        ListNode* prev = NULL;        while(l1 || l2 || carry) {            int num1 = l1 ? l1->val : 0;            int num2 = l2 ? l2->val : 0;            int sum = num1 + num2 + carry;            ListNode* node = new ListNode(sum%10);            if(!head) head = node;            if(prev) prev->next = node;            prev = node;            carry = sum / 10;            if(l1) l1 = l1->next;            if(l2) l2 = l2->next;        }        return head;    }};