题解 | #两个链表生成相加链表#

import java.util.*;

public class Solution {
    public ListNode addInList (ListNode head1, ListNode head2) {
        ListNode h1 = reverse(head1), h2 = reverse(head2);
        ListNode dummy = new ListNode(-1);
        ListNode cursor = dummy;
        int carry = 0;
        while(h1 != null || h2 != null || carry != 0){
            int h1Val = h1 == null ? 0 : h1.val;
            int h2Val = h2 == null ? 0 : h2.val;
            int sum = h1Val + h2Val + carry;
            ListNode node = new ListNode(sum % 10);
            carry = sum / 10;
            cursor.next = node;
            cursor = node;
            if(h1 != null) h1 = h1.next;
            if(h2 != null) h2 = h2.next;
        }
        return reverse(dummy.next);
    }
    
    public ListNode reverse(ListNode head){
        ListNode pre = null;
        ListNode cur = head;
        ListNode temp = null;
        while(cur != null){
            temp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = temp;
        }
        return pre;
    }
}