Invert a binary tree.
Example:
Input:
4
/ \
2 7
/ \ / \
1 3 6 9
Output:
4
/ \
7 2
/ \ / \
9 6 3 1
Trivia:
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 f*** off.
"经典"的反转二叉树的问题。
还是用递归来解决,先递归调用反转根节点的左孩子,然后递归调用反转根节点的右孩子,然后左右交换根节点的左孩子和右孩子。