2. 两数相加
模拟。
/**
* 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 *head = nullptr, *tail = nullptr;
int carry = 0; // 进位
while(l1 || l2 || carry)
{
int t = carry;
if(l1) t += l1->val, l1 = l1->next;
if(l2) t += l2->val, l2 = l2->next;
ListNode* node = new ListNode(t % 10);
if(!tail) head = tail = node;
else tail->next = node, tail = node;
carry = t / 10;
}
return head;
}
};