题解 | #两个链表生成相加链表#

思路：大数相加+链表反转

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) {
        // write code here
        ListNode ans = new ListNode(-1);
        ListNode p = ans;
        int pre = 0;
        head1 = reverse(head1);


        head2 = reverse(head2);

        while(head1!=null&&head2!=null){
            int sum = head1.val+head2.val + pre;
            pre = sum/10;
            p.next = new ListNode(sum%10);
            p = p.next;
            head1 = head1.next;
            head2 = head2.next;
        }
        while(head1!=null){
            int sum = head1.val+pre;
            pre = sum/10;
            p.next = new ListNode(sum%10);
            p = p.next;
            head1 = head1.next;
        }
        while(head2!=null){
            int sum = head2.val+pre;
            pre = sum/10;
            p.next = new ListNode(sum%10);
            p = p.next;
            head2 = head2.next;
        }
        if(pre == 1){
            p.next = new ListNode(1);
        }
        //翻转链表
        return reverse(ans.next);

    }
    public ListNode reverse(ListNode head){
        //ListNode p = head;
        ListNode pre = null;
        while(head!=null){
            ListNode next = head.next;
            head.next = pre;
            pre = head;
            head = next;
        }
        return pre;
    }
}