226. Invert Binary Tree

Given the root of a binary tree, invert the tree, and return its root.

Example 1:

1 2	Input: root = [4,2,7,1,3,6,9] Output: [4,7,2,9,6,3,1]

Example 2:

1 2	Input: root = [2,1,3] Output: [2,3,1]

Example 3:

1 2	Input: root = [] Output: []

遞迴反轉

T:O(2ˆn) S:O(n)
class Solution:
    def invertTree(self, root: TreeNode) -> TreeNode:
        if not root: return None       
        root.left, root.right = self.invertTree(root.right), self.invertTree(root.left)
        return root

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