leetcode 2. Add Two Numbers(java递归解法)

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.

方法一、递归，网上没有找到好的递归方法，所以自己实现。思路很简单，看代码就懂了。缺点：时间和空间复杂度较高。

代码：

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        return addTwoNumbers(l1, l2, 0);
    }
    public ListNode addTwoNumbers(ListNode l1, ListNode l2, int carry) {
        if(l1 == null && l2 == null && carry == 0){
            return null;
        }
        if(l1 == null) l1 = new ListNode(0);
        if(l2 == null) l2 = new ListNode(0);
        int temp = carry + l1.val + l2.val;
        carry = temp / 10;
        l1.val = temp % 10; 
        l1.next = addTwoNumbers(l1.next, l2.next, carry);
        return l1;
    }
}