題目描述
翻轉一棵二叉樹。
示例:
輸入:
4
/ \
2 7
/ \ / \
1 3 6 9
輸出:
合併後的樹:
4
/ \
7 2
/ \ / \
9 6 3 1
來源:力扣(LeetCode)
鏈接:https://leetcode-cn.com/problems/invert-binary-tree/
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解題方法和思路
遞歸翻轉
思路和合並二叉樹的思路非常相似,利用遞歸實現,要實現翻轉功能可以分爲一下幾步:
- 該節點不空則進行一下步驟,否則返回None
- 翻轉左子樹
- 翻轉右子樹
- 交換左右孩子節點
核心代碼:
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def invertTree(self, root: TreeNode) -> TreeNode:
if root is None:
return None
root.left ,root.right = self.invertTree(root.right), self.invertTree(root.left)
return root
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def invertTree(self, root: TreeNode) -> TreeNode:
if root is not None:
root.left ,root.right = self.invertTree(root.right), self.invertTree(root.left)
return root