題目
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 contain a single digit. Add the two numbers and return it as a linked list.

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

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

Explanation: 342 + 465 = 807.

答案

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode l3 = new ListNode(0);
        ListNode ret = l3;
        int sum, num, carry = 0;
        while(l1 != null || l2 != null) {
            sum = ((l1 != null)?l1.val:0) + ((l2 != null)?l2.val:0) + carry;
            num = sum % 10;
            carry = (sum >= 10)? 1:0;
            
            if(l1 != null) l1 = l1.next;
            if(l2 != null) l2 = l2.next;
            
            l3.val = num;
            if(l1 != null || l2 != null)
                l3.next = new ListNode(0);
            else
                if(carry != 0) l3.next = new ListNode(1);
            l3 = l3.next;
        }
        return ret;
    }
}