特定深度节点链表. Python 练习一遍 map + reduce

class Solution:
    def listOfDepth(self, tree: TreeNode) -> List[ListNode]:

        def fun(x,y):
            x.next = y
            return x.next #要return，后面能用reduce，希望什么作为x传入下一次迭代呢？当然是当前链表的尾结点，即 y

        def getList(a): #传入一个 list a = [1,2,3]
            nodes = list(map(lambda x:ListNode(x),a)) #[1,2,3]转为ListNode类型
            tail = reduce(fun,nodes) # lambda 好像并不能类似赋值，只能自定义函数了
            tail.next = None
            return nodes[0]

        # 主函数域
        res = []
        q = []
        q.insert(0,tree)

        while q:
            size = len(q)
            a = []
            while size:
                out = q.pop()
                a.append(out.val)

                if out.left:
                    q.insert(0,out.left)
                if out.right:
                    q.insert(0,out.right)

                size -= 1

            cur_list = getList(a)
            res.append(cur_list)
        return res