Problem Definition:　　

　　Invert a binary tree.

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

　　to

4   /   \  7     2 / \   / \9   6 3   1 Trivia: This problem was inspired by  by :

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.

1 class Solution: 2     # @param {TreeNode} root 3     # @return {TreeNode} 4     def invertTree(self, root): 5         if root==None: 6             return root 7         root.left,root.right=root.right,root.left 8         self.invertTree(root.left) 9         self.invertTree(root.right)10         return root