T1:leetcode.2 两数相加

/**
 * 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) {
        ListNode* dummy = new ListNode(0);
        ListNode* cur = dummy;
        int carry = 0;
        while (l1 != nullptr || l2!= nullptr || carry) {
            if (l1 != nullptr) carry += l1->val;
            if (l2 != nullptr) carry += l2->val;
            ListNode* tmp = new ListNode(carry % 10);
            cur -> next = tmp;
            cur = cur -> next;
            if (l1 != nullptr) l1 = l1 -> next;
            if (l2 != nullptr) l2 = l2 -> next;
            carry /= 10;
        }
        return dummy->next;
    }
};
/*
1.设置虚头节点 返回dummy->next
2.用cur代替dummy
3.引入carry存储进1的值
*/
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