AddTwoNumbers.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class AddTwoNumbers {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummp = new ListNode(0);
        ListNode tail = dummp;
        int carry = 0;
        while (l1 != null || l2 != null) {
            int d1 = l1 == null ? 0 : l1.val;
            int d2 = l2 == null ? 0 : l2.val;
            int sum = d1 + d2 + carry;
            int d = sum % 10;
            carry = sum / 10;
            tail.next = new ListNode(d);
            tail = tail.next;
            if (l1 != null) l1 = l1.next;
            if (l2 != null) l2 = l2.next;
        }
        if (carry > 0) tail.next = new ListNode(carry);
        return dummp.next;

    }
}