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

Example 1:

invert1-tree

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

Example 2:

invert2-tree

  • 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