leetcode-----2. 两数相加

• 链接：https://leetcode-cn.com/problems/add-two-numbers/

算法

时间复杂度：(O(n))

代码

/**
 * 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* ans = nullptr;
        ListNode* cur = nullptr;
        int carry = 0;
        while (l1 != nullptr || l2 != nullptr || carry != 0) {
            carry += (l1 == nullptr ? 0 : l1->val) + (l2 == nullptr ? 0 : l2->val);
            auto tmp = new ListNode(carry % 10);
            carry /= 10;
            if (ans == nullptr) {
                ans = tmp;
                cur = ans;
            } else {
                cur->next = tmp;
                cur = cur->next;
            }
            l1 = l1 == nullptr ? 0: l1->next;
            l2 = l2 == nullptr ? 0: l2->next;
        }
        return ans;
    }
};