LeetCode 2 - Add Two Numbers

原题如下：

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

题目比较简单，需要注意边界情况的处理和链表指针的使用，代码如下：

class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
        next = null;
    }
}

public class AddTwoNumbers2 {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode head = null;
        ListNode ll1 = l1;
        ListNode ll2 = l2;
        int res = 0;
        ListNode cur = null;
        while (true) {
            int curval = 0;
            curval += res;
            if (ll1 == null && ll2 == null) {
                if (curval != 0) {
                    cur.next = new ListNode(curval);
                }
                break;
            }
            if (ll1 != null) {
                curval += ll1.val;
                ll1 = ll1.next;
            }
            if (ll2 != null) {
                curval += ll2.val;
                ll2 = ll2.next;
            }
            if (curval >= 10) {
                res = 1;
                curval -= 10;
            } else {
                res = 0;
            }
            if (cur == null) {
                head = cur = new ListNode(curval);
            } else {
                cur.next = new ListNode(curval);
                cur = cur.next;
            }
        }
        return head;
    }
}

参考源码：https://github.com/pkufork/Martians/blob/master/src/main/java/com/pkufork/martians/leetcode/L2_AddTwoNumbers.java