/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode() {}

* TreeNode(int val) { this.val = val; }

* TreeNode(int val, TreeNode left, TreeNode right) {

* this.val = val;

* this.left = left;

* this.right = right;

* }

* }

*/

class Solution {

// 풀이: child node로 내려가면서 재귀로 계속 left와 right를 바꿔준다.

// TC: O(N)

// SC: O(N)

public TreeNode invertTree(TreeNode root) {

return invert(root);

}

private TreeNode invert(TreeNode node) {

if (node == null) {

return node;

}

node = swap(node);

invert(node.left);

invert(node.right);

return node;

}

private TreeNode swap(TreeNode node) {

var temp = node.left;

node.left = node.right;

node.right = temp;

return node;

}

}