[LeetCode] Add Two Numbers

Problems:

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

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Solution: O(n)

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
      int carry = 0;
      if(l1 == null)
         return l2;
         
      if(l2 == null)
         return l1;
      ListNode ret = null;
      ListNode cur = ret;
      while(l1!=null || l2!=null){
         int left = 0;
         int right = 0;
         if(l1 !=null){
             left = l1.val;
             l1 = l1.next;
         }
         if(l2 !=null){
             right = l2.val;
             l2 = l2.next;
         }
         int sum = left + right+ carry;
         carry = sum/10;
         if(ret == null){
             ret = new ListNode(sum%10);
             cur = ret;
         }else{
          cur.next = new ListNode(sum%10);
          cur = cur.next;
         }
      }
      if(carry >0)
       cur.next = new ListNode(carry);
      
         return ret;
     }
}