题解 | #链表相加(二)#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head1 ListNode类
     * @param head2 ListNode类
     * @return ListNode类
     */
    public ListNode addInList (ListNode head1, ListNode head2) {
        if (head1 == null) {
            return head2;
        }

        if (head2 == null) {
            return head1;
        }

        ListNode head1R = reverse(head1);
        ListNode head2R = reverse(head2);

        ListNode newHead = new ListNode(-1);
        ListNode curNode = newHead;

        int jinwei = 0;
        while (head1R != null || head2R != null) {
            int val = jinwei;
            if (head1R != null) {
                val += head1R.val;
                head1R = head1R.next;
            }
            if (head2R != null) {
                val += head2R.val;
                head2R = head2R.next;
            }
            jinwei = val / 10;
            curNode.next = new ListNode(val % 10);
            curNode = curNode.next;
        }
        if (jinwei > 0) {
            curNode.next = new ListNode(jinwei);
        }

        return reverse(newHead.next);
    }

    public ListNode reverse(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode curNode = head;
        ListNode preNode = null;
        while (curNode != null) {
            ListNode nextNode = curNode.next;
            curNode.next = preNode;
            preNode = curNode;

            curNode = nextNode;
        }
        return preNode;
    }
}