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import java.util.LinkedList;

import java.util.Queue;

/**

* 给非递归法也要会写

* 核心思路就是访问所有的节点，将其左右节点交换，可以采用递归，也可以BFS

*/

public class InvertBinaryTree {

public TreeNode invertTree(TreeNode root) {

if (root == null) {

return null;

}

TreeNode right = root.right;

root.right = invertTree(root.left);

root.left = invertTree(right);

return root;

}

public TreeNode invertTree2(TreeNode root) {

if (root == null) {

return null;

}

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

queue.offer(root);

while (!queue.isEmpty()) {

TreeNode node = queue.poll();

TreeNode left = node.left;

node.left = node.right;

node.right = left;

if (node.left != null) {

queue.offer(node.left);

}

if (node.right != null) {

queue.offer(node.right);

}

}

return root;

}

}