226. Invert Binary Tree

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.

Analyze

递归调换左右子节点的位置。

/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {TreeNode}
*/
var invertTree = function(root) {
if (!root) return null
if (root.left || root.right) {
const tmp = root.left
root.left = root.right
root.right = tmp
invertTree(root.left)
invertTree(root.right)
}
return root
};