題目:

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

給定一棵二元樹,將其左右反轉後回傳

透過簡單的遞迴,這題不算太難

# 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]:
        if not root: #防止root即為None
            return None
            
        temp=root.right
        root.right=root.left
        root.left=temp
        root.right=self.invertTree(root.right)
        root.left=self.invertTree(root.left)
        return root

將root的左右枝互換
接著再透過遞迴向下,將root的左右枝之左右枝互換
直到碰到None為止
工程全部結束後,我們便得到一棵反轉完的binary tree了
最後執行時間30ms(faster than 95.51%)

那我們下題見