(Leet Code c++)Add Two Numbers

2. Add Two Numbers

 

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

 

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4] Output: [7,0,8] Explanation: 342 + 465 = 807.

 

Example 2:

Input: l1 = [0], l2 = [0] Output: [0]

 

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9] Output: [8,9,9,9,0,0,0,1]

 

Constraints:

• The number of nodes in each linked list is in the range [1, 100].
• 0 <= Node.val <= 9
• It is guaranteed that the list represents a number that does not have leading zeros.

/**
 * 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) {
        int sum = 0;
        ListNode *head = NULL;
        ListNode **current = &head;
        
        while(l1 != NULL || l2 != NULL || sum > 0){
            if(l1 != NULL){
                sum += l1->val;
                l1 = l1->next;
            }
            
            if(l2 != NULL){
                sum += l2->val;
                l2 = l2->next;
            }
            
            (*current) = new ListNode(sum % 10);
            sum /= 10;
            current = &((*current)->next);
        }
        
        return head;
    }
};