c_cpp 2.添加两个数字 - 中 - 2018.8.7

Posted 2021-05-14

/**
 * 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) {
        if (l1 == NULL) return l2;
        if (l2 == NULL) return l1;
        
        int carry = 0;
        ListNode *resultNode = l1;
        while (l1 && l2) {
            l1 -> val += (l2 -> val + carry);
            if (l1 -> val >= 10) {
                carry = 1;
                l1 -> val -= 10;
            } else {
                carry = 0;
            }
            if (l1 -> next 
                && l2 -> next) {
                l1 = l1 -> next;
                l2 = l2 -> next;
            } else {
                break;
            }
        }
        
        if (carry == 0
            && l1 -> next == NULL
            && l2 -> next == NULL) 
            return resultNode;
        
        if (l1 -> next == NULL
            && l2 -> next == NULL) {
            l1 -> next = new ListNode(0);
        } else if (l1 -> next == NULL) {
            l1 -> next = l2 -> next; 
        }
        l1 = l1 -> next;
        
        while(carry) {
            l1 -> val += carry;
            if (l1 -> val >= 10) l1 -> val -= 10;
            else break;
            if (l1 -> next == NULL) {
                l1 -> next = new ListNode(0);
            }
            l1 = l1 -> next;
        }
        
        return resultNode;
    }
};