Problem

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.

Constraints:

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

Example1

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

Example2

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

Example3

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

Solution

/** * 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 && !l2) return NULL; else if(l1 && !l2) return l1; else if(!l1 && l2) return l2; ListNode dummy; ListNode *cur = &dummy; int carry = 0; while(l1 || l2 || carry) { int sum = (l1?l1->val:0) + (l2?l2->val:0) + carry; int val = sum % 10; carry = sum /10; cur->next = new ListNode(val); cur = cur->next; if(l1) l1 = l1->next; if(l2) l2 = l2->next; } return dummy.next; } };