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 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;
}