2_add_two_numbers.cpp

//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) {
        ListNode* head = new ListNode(0);
        ListNode* current = head;
        int link = 0;
        while (l1 != NULL || l2 != NULL || link != 0) {
            int x = l1 ? l1->val : 0;
            int y = l2 ? l2->val : 0;
            
            int sum = link + x + y;
            
            link = sum / 10;
            current->next = new ListNode(sum % 10);
            current = current->next;
            l1 = l1 ? l1->next : nullptr;
            l2 = l2 ? l2->next : nullptr;
        }
        
        return head->next;
    }
};