[LeetCode] 2. Add Two Numbers

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

Time Complexity: O(max(m,n))

Space Complexity: O(max(m,n))

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy=new ListNode(0);
        ListNode tail=dummy;
        int carry=0;
        if(l1==null) return l2;
        if(l2==null) return l1;
        
        while(l1!=null||l2!=null){
            if(l1!=null){
                carry+=l1.val;
                l1=l1.next;
            }
            if(l2!=null){
                carry+=l2.val;
                l2=l2.next;
            }
            tail.next=new ListNode(carry%10);
            tail=tail.next;
            carry/=10;
        }
        if(carry==1){
            tail.next=new ListNode(1);
        }
        return dummy.next;
    }
}