Problem

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

Example 1:

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

Example 2:

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

Example 3:

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Input: root = []
Output: []

Constraints:

  • The number of nodes in the tree is in the range [0, 100].
  • 100 <= Node.val <= 100

Solve

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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
class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:
        def invert(node):
            if not node:
                return None
            node.left , node.right = node.right , node.left  #交換
						#如果還有就繼續做
            if node.left:
                invert(node.left)
            if node.right:
                invert(node.right)
            return node
        
        return invert(root)
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class Solution:
    def invertTree(self, root: Optional[TreeNode]) -> Optional[TreeNode]:

        if not root:
            return root
        
        left = root.left
        right = root.right
        root.left , root.right = self.invertTree(root.right) ,self.invertTree(root.left)
        
        return root