在二叉树中增加一行

/*
 * Problem: Add a row of nodes with value val at the given depth in a binary tree.
 * Input: root - the root of the tree, val - the value of the new nodes, depth - the depth where the new nodes are added.
 * Output: The modified tree root after adding the new nodes.
 * 
 * Approach:
 * 1. If depth == 1, create a new root node with value val, and set the original tree as its left child.
 * 2. Use a Stream to iterate over the nodes, collecting them at depth - 1.
 * 3. For each collected node, create two new nodes with value val as the left and right children.
 * 4. Set the original left and right children of the node as the children of the newly created nodes respectively.
 */
 
public TreeNode addOneRow(TreeNode root, int val, int depth) {
    if (depth == 1) {
        TreeNode newRoot = new TreeNode(val);
        newRoot.left = root;
        return newRoot;
    }
    List<TreeNode> nodesAtDepth = new ArrayList<>();
    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    int currentDepth = 1;
    while (!queue.isEmpty() && currentDepth < depth - 1) {
        int size = queue.size();
        for (int i = 0; i < size; i++) {
            TreeNode node = queue.poll();
            if (node.left != null) queue.offer(node.left);
            if (node.right != null) queue.offer(node.right);
        }
        currentDepth++;
    }
    nodesAtDepth = queue.stream().collect(Collectors.toList());
    nodesAtDepth.forEach(node -> {
        TreeNode newLeft = new TreeNode(val);
        TreeNode newRight = new TreeNode(val);
        newLeft.left = node.left;
        newRight.right = node.right;
        node.left = newLeft;
        node.right = newRight;
    });
    return root;
}