226 Invert Binary Tree.js

/**
 * 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.
 *
 * Invert a binary tree.
 * 翻转一棵二叉树。
 */

/**
 * Example:
 * Input:
 *      4
 *    /   \
 *   2     7
 *  / \   / \
 * 1   3 6   9
 *
 * Output:
 *      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}
 */
const invertTree = (root) => {
  if (Object.prototype.toString.call(root) === '[object Array]') {
    return root
  }
  if (root === null) {
    return root
  }

  let tmp = root.left
  root.left = root.right
  root.right = tmp

  invertTree(root.left)
  invertTree(root.right)

  return root
}