翻转二叉树

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

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

/**
 * 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 root;
    invertTree(root.left);
    invertTree(root.right);
    [root.left, root.right] = [root.right, root.left];
    return root;
};

https://github.com/WindrunnerMax/EveryDay

https://leetcode-cn.com/problems/invert-binary-tree/