2. 两数相加

2. 两数相加

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummyHead = new ListNode(-1);
        ListNode node = dummyHead;
        int carry = 0;
        while (l1 != null || l2 != null) {
            int sum = 0;
            int x = l1 == null ? 0 : l1.val;
            int y = l2 == null ? 0 : l2.val;
            sum = x + y + carry;
            carry = sum / 10;
            sum = sum % 10;
            node.next = new ListNode(sum);
            node = node.next;
            if (l1 != null) l1 = l1.next;
            if (l2 != null) l2 = l2.next;
        }

        if (carry != 0) {
            node.next = new ListNode(1);
        }
        return dummyHead.next;
    }
}

。。