Problem Description

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

Examples

Example 1:

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

Example 2:

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

Example 3:

Input: root = []
Output: []

Constraints:

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

解析

題目給定一個二元樹的 root

實作一個演算法把數中所有原本左邊的結點換成右邊的結點

已知每個結點都由左結點與右邊結點組成

所以 要反轉整個樹的左右結點等於 把root 的左右結點互換 + 原本左子樹做反轉 + 原本右子樹做反轉