题解 | #两个链表生成相加链表#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @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;   
        }

        int temp = 0;
        ListNode curNode1 = reverseListNode(head1);
        ListNode curNode2 = reverseListNode(head2);
        ListNode head = new ListNode(-1);
        ListNode tempNode = head;

        while(curNode1!=null || curNode2!=null || temp!=0){

            if(curNode1!=null){
                temp += curNode1.val;
                curNode1 = curNode1.next;
            }

            if(curNode2!=null){
                temp += curNode2.val;
                curNode2 = curNode2.next;
            }

            ListNode node = new ListNode(temp%10);
            temp = temp/10;
            head.next = node;
            head = node;
        }

        return reverseListNode(tempNode.next);
    }

    public ListNode reverseListNode(ListNode head){

        ListNode curNode = head.next;
        ListNode preNode = head;
        ListNode tempNode = null;

        while(curNode!=null){
            tempNode = curNode.next;
            curNode.next = preNode;
            preNode = curNode;
            curNode = tempNode;
        }

        head.next = null;

        return preNode;
    }
}