leetcode 2. 两数相加

题目：2. 两数相加 - 力扣（LeetCode）

水题

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        int y = 0;
        ListNode* ret = nullptr;
        ListNode* tail = nullptr;
        while (l1 || l2 || y) {
            int a = 0, b = 0;
            if (l1) {
                a = l1->val;
                l1 = l1->next;
            }
            if (l2) {
                b = l2->val;
                l2 = l2->next;
            }
            ListNode* t = new ListNode;
            t->val = (a + b + y) % 10;
            y = (a + b + y) / 10;
            if (!tail) {
                ret = t;
                tail = t;
            } else {
                tail->next = t;
                tail = t;
            }
        }
        
        return ret;
    }
};