445. adding two numbers II

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subject ：445. Addition of two numbers II The finger of the sword Offer II 025. The two numbers in the linked list are added
describe ： Here are two for you Non empty The list represents two nonnegative integers . The highest digit is at the beginning of the list . They store only one digit per node . Adding these two numbers will return a new linked list .

You can assume that in addition to the numbers 0 outside , Neither of these numbers starts with zero .

Their thinking

1、 Reverse the two linked lists and add them ;
2、 Pay attention to carry jinwei;
3、 Pay attention to judge whether the linked list is empty or has come to the end ;

Source code ##

class Solution {
    
public:
    ListNode *reverseList(ListNode *head) {
    
        if (head == nullptr || head->next == nullptr) return head;
        ListNode *pre = nullptr;
        ListNode *cur = head;
        while (cur) {
    
            ListNode *temp = cur->next;
            cur->next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
    
        ListNode *l11 = reverseList(l1);
        ListNode *l12 = reverseList(l2);
        ListNode *p = new ListNode(-1);
        ListNode *ans = p;
        int jinwei = 0;
        while (l11 || l12) {
    
            int num1 = l11 ? l11->val : 0;
            int num2 = l12 ? l12->val : 0;
            int sum = num1 + num2 + jinwei;
            p->next = new ListNode(sum % 10);
            jinwei = sum / 10;
            if (l11) l11 = l11->next;
            if (l12) l12 = l12->next;
            p = p->next;
        }
        if (jinwei) p->next = new ListNode(jinwei);
        return reverseList(ans->next);
    }
};