反转二叉树

方式一: 递归实现

TreeNode invertTree(TreeNode node) {
	if (node == null) {
		return null;
	}
	TreeNode temp = node.left;
	node.left = node.right;
	node.right = temp;
	invertTree(node.left);
	invertTree(node.right);
	return node;
}

方式二: 队列实现

TreeNode invertTree(TreeNode root) {
	if (root == null) {
		return null;
	}
	Queue<TreeNode> queue = new LinkedList<>();
	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;
}