Invert Binary Tree

Given the root of a binary tree, invert the tree (mirror it), and return its root.

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Example 1

Input:
        4
       / \
      2   7
     / \ / \
    1  3 6  9

Output:
        4
       / \
      7   2
     / \ / \
    9  6 3  1

Input: root = [4,2,7,1,3,6,9]
Output: [4,7,2,9,6,3,1]
Explanation: Every node's left and right children are swapped throughout the entire tree.

Example 2

Input: root = [2,1,3]
Output: [2,3,1]
Explanation: The root's two children are swapped.

Example 3

Input: root = []
Output: []
Explanation: An empty tree inverted is still empty.

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Constraints

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