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public class ListOfDepth {

    public static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int x) {
            val = x;
        }
    }

    public static class ListNode {
        int val;
        ListNode next;

        ListNode(int x) {
            val = x;
        }
    }
    public ListNode[] listOfDepth(TreeNode tree) {
        //递归计算出树的深度
        int depth = getDepth(tree);
        //初始化保存路径数组
       ListNode[] listNodes = new ListNode[depth];
        //采用队列临时存放树上每一层的节点
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(tree);
        int index = 0;
        //循环终止条件：树的最大深度
        while (!queue.isEmpty()) {
            int size = queue.size();
            ListNode newhead = new ListNode(0);
            ListNode indexNode = newhead;
            for (int i = 0; i < size; i++) {
                TreeNode poll = queue.poll();
                indexNode.next = new ListNode(poll.val);
                indexNode = indexNode.next;
                if (poll.left != null) {
                    queue.offer(poll.left);
                }
                if (poll.right != null) {
                    queue.offer(poll.right);
                }
            }
            listNodes[index++] = newhead.next;
        }
        return listNodes;
    }
    private int getDepth(TreeNode treeNode) {
        if (treeNode == null) {
            return 0;
        }
        return Math.max(getDepth(treeNode.left), getDepth(treeNode.right)) + 1;
    }
}