题解 | #两个链表生成相加链表#

反转链表 再计算

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

public class Solution {
    /**
     * 
     * @param head1 ListNode类 
     * @param head2 ListNode类 
     * @return ListNode类
     */
        int carry = 0;

    public ListNode addInList (ListNode head1, ListNode head2) {
        // write code here
        ListNode list1  = reverseListNode(head1);
        ListNode list2 = reverseListNode(head2);
        ListNode curr1  = list1;
        ListNode curr2 = list2;
        ListNode guardNode = new ListNode(-1);
        ListNode curr3 = guardNode;
        while (curr1 != null || curr2 != null|| carry!=0){
            int val1 = curr1 != null? curr1.val:0;
            int val2 = curr2 != null? curr2.val:0;
            int sum  = val1 + val2+carry;
            carry = sum/10;
            int temp  = sum%10;
            ListNode node = new ListNode(temp);
            curr3.next = node;
            curr3 = node;
            if(curr1 != null){
                   curr1 = curr1.next;
            }
            if(curr2 != null){
                curr2 = curr2.next;
            }
        }
        ListNode headNode = guardNode.next;
        ListNode resNode = reverseListNode(headNode);
        return  resNode;
    }

    public  ListNode reverseListNode (ListNode head){
        if (head == null){
            return  head;
        }
        ListNode prev = null;
        ListNode curr = head;
        while (curr != null){
            ListNode nextNode = curr.next;
            curr.next = prev;
            prev = curr;
            curr = nextNode;
        }
        return  prev;
    }
}