Python版day15

102. 二叉树的层序遍历

给你二叉树的根节点 root ，返回其节点值的 层序遍历 。 （即逐层地，从左到右访问所有节点）。 

 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        if not root:
            return []
        queue = deque()
        res = []
        queue.append(root)
        while queue:
            size = len(queue)
            temp = []
            for i in range(size):
                node = queue.popleft()
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
                temp.append(node.val)
            res.append(temp)
        return res

226. 翻转二叉树

给你一棵二叉树的根节点 root ，翻转这棵二叉树，并返回其根节点。 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        return self.invertHelper(root)
    def invertHelper(self,node):
        if not node:
            return node
        if not node.left and not node.right:
            return node
        left = node.left
        right = node.right
        node.left =self.invertHelper(right)
        node.right = self.invertHelper(left)
        return node

 101. 对称二叉树

给你一个二叉树的根节点 root ， 检查它是否轴对称。 

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        return self.helper(root.left,root.right)
    def helper(self,left,right):
        if not left and not right:
            return True
        if not left and right:
            return False
        if left and not right:
            return False
        if left.val != right.val:
            return False
        inside = self.helper(left.right,right.left)
        outside = self.helper(left.left,right.right)
        return inside and outside