合并两个链表出错

Question

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        root = ListNode(x=None)
        cur = root
        while l1 and l2:
            if l1.val <= l2.val:
                cur.val = l1.val
                cur.next = temp_node = ListNode(x=None)
                cur = temp_node
                l1 = l1.next
            else:
                cur.val = l2.val
                cur.next = temp_node = ListNode(x=None)
                cur = temp_node
                l2 = l2.next
        if l1:
            cur.val = l1.val
            cur.next = l1.next
        else:
            cur.val = l2.val
            cur.next = l2.next
        return root

老师您看一下我的代码哪里出错 了，在Leetcode上运行的时候是可以的，提交的时候就出现内部出错。请问哪里错了呢？

Answer 1

PegasusWang 2019-03-24 23:46:05

你提交的时候是可以看到错误的用例的。

考虑下当输入两个空链表的情况，代码会直接走到 这里，因为 l2 是 None，直接抛异常了

else:
            cur.val = l2.val
            cur.next = l2.next

AttributeError: 'NoneType' object has no attribute 'val' 

Line 20 in mergeTwoLists (Solution.py) 

Line 66 in main (Solution.py) 

Line 74 in <module> (Solution.py)