226. 翻转二叉树.md

翻转一棵二叉树。

示例：

输入：

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

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

solution:

/**
 * 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 temp = invertTree(root.left)
        root.left = invertTree(root.right)
        root.right = temp
        return root
    } else {
        return root
    }
};

还有一种更巧妙的方法，利用了解构赋值的特性，省去了temp的临时变量存储

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