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Leetcode 226 翻转二叉树

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翻转一棵二叉树。

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# 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
# 递归
class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if not root:
            return 
        root.left, root.right = root.right, root.left
        self.invertTree(root.left)
        self.invertTree(root.right)
        return root
    
# 迭代
class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        if not root:
            return
        stack = [root]
        while stack:
            cur = stack.pop()
            cur.left, cur.right = cur.right, cur.left
            if cur.left: stack.append(cur.left)
            if cur.right: stack.append(cur.right)
        return root