nvert a binary tree.     4   /   \  2     7 / \   / \1   3 6   9to     4   /   \  7     2 / \   / \9   6 3   1Trivia:This problem was inspired by this original tweet by Max Howell:Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

Of course use Recursion, on each level, have the root.left switch to right and root.right switch to left

1 public class Solution {2     public TreeNode invertTree(TreeNode root) {3         if (root == null) return null;4         TreeNode left = root.left;5         root.left = invertTree(root.right);6         root.right = invertTree(left);7         return root;8     }9 }