import java.util.ArrayDeque;

import java.util.Queue;

/**

* 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;

* }

* }

*/

//시간복잡도: O(n)

//공간복잡도: O(n)

class Solution {

public TreeNode invertTree(TreeNode root) {

if(root == null) {

return root;

}

Queue<TreeNode> queue = new ArrayDeque<>();

queue.add(root);

while(!queue.isEmpty()) {

TreeNode cur = queue.poll();

if(cur == null) {

continue;

}

TreeNode temp = cur.left;

cur.left = cur.right;

cur.right = temp;

if(cur.left != null) {

queue.add(cur.left);

}

if(cur.right != null) {

queue.add(cur.right);

}

}

return root;

}

}