链接：链表相加(二)_牛客题霸_牛客网 (nowcoder.com)

分析：

算法原理是逆序+高精度算法

逆序的原因是为了实现从低位（个位）开始相加。

public class Solution {//逆序链表public ListNode reverse(ListNode head){ListNode newHead = new ListNode(0);ListNode cur = head;while(cur != null){ListNode next = cur.next;cur.next = newHead.next;newHead.next = cur;cur = next;}return newHead.next;}public ListNode addInList (ListNode head1, ListNode head2) {//调用reverse()方法，以便从低位相加head1 = reverse(head1);head2 = reverse(head2);ListNode cur1 = head1;ListNode cur2 = head2;//t用来存储进位int t = 0;//ret作为头节点，prev初始化ret作为最终结果链表ListNode ret = new ListNode(0);ListNode prev = ret;while(cur1 != null || cur2 != null || t != 0){if(cur1 != null){t += cur1.val;cur1 = cur1.next;}if(cur2 != null){t += cur2.val;cur2 = cur2.next;}prev = prev.next = new ListNode(t % 10);t /= 10;}return reverse(ret.next);}
}