c_cpp 2.添加两个数字

Posted 2021-05-14

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
 // without extra space
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        if (!l2) return l1;
        ListNode *h1 = l1, *h2 = l2, *prev=nullptr;
        int carry = 0;
        while (h1 || h2 || carry) {
            int result = carry;
            if (h1) {
                result += h1->val;
            }
            if (h2) {
                result += h2->val;
            };
            carry = result / 10;
            result %= 10;
            if (!h2) {
                h2 = new ListNode(result);
                prev->next = h2;
            } else {
                h2->val = result;
            }
            prev = h2;  
            if (h1) h1 = h1->next;
            h2 = h2->next;
        }
        return l2;
    }
};