二叉搜索树（2）

class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root: return []
        res, queue = [], collections.deque()
        queue.append(root)
        while queue:
            tmp = []
            for _ in range(len(queue)):
                node = queue.popleft()
                tmp.append(node.val)
                if node.left: queue.append(node.left)
                if node.right: queue.append(node.right)
            res.append(tmp[::-1] if len(res) % 2 else tmp)
        return res

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root: return []
        res, stack = [],[root]
        while stack:
            tmp = []
            for _ in range(len(stack)):
                node = stack.pop(0)
                if len(res) &1: tmp.insert(0,node.val) # 偶数层 -> 队列头部
                else: tmp.append(node.val) # 奇数层 -> 队列尾部
                if node.left: stack.append(node.left)
                if node.right: stack.append(node.right)
            res.append(list(tmp))
        return res

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root: return []
        res, stack = [],[root]
        while stack:
            tmp = []
            for _ in range(len(stack)):
                node = stack.pop(0)
                tmp.append(node.val) # 奇数层 -> 队列尾部
                if node.left: stack.append(node.left)
                if node.right: stack.append(node.right)
            res.append(tmp[::-1] if len(res)&1 else tmp)
            
        return res