题解 | 链表相加(二)

1.通过反转链表的方式，可以让他们从头开始算

2.累加完后，再次反转。

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) {
        ListNode temp = fanzhuan(head1);
        ListNode new2 = fanzhuan(head2);

        ListNode cur = new ListNode(-1);
        ListNode pre = cur;
        int i=0;
        while(temp !=null || new2 != null || i==1) {
            int val = i;
            if (temp != null) {
                val += temp.val;
                temp = temp.next;
            }
            if (new2 != null) {
                val += new2.val;
                new2 = new2.next;
            }
            i = 0;
            if (val >= 10) {
                i = 1;
                val -= 10;
            }
            
            pre.next = new ListNode(val);
            pre = pre.next;
        }
        return fanzhuan(cur.next);
    }

    public ListNode fanzhuan(ListNode node) {
        ListNode cur = node;
        ListNode pre = null;

        while(cur != null){
            ListNode temp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }

}