【Java】创建二叉树，从上至下打印二叉树

  /**
     * 二叉树的生成
     */


    public static ArrayList<ArrayList<Object>> PrintFromTopToBottom(TreeNode root) {
        Queue<TreeNode> queue = new LinkedList<>();
        ArrayList<ArrayList<Object>> ret = new ArrayList<>();

        queue.add(root);
        while (!queue.isEmpty()) {
            int cnt = queue.size();
            ArrayList<Object> arr = new ArrayList<>();
            while (cnt-- > 0) {
                TreeNode t = queue.poll();
//                if (t == null || t.data.equals("#"))
//                    continue;

                arr.add(t.data);

                queue.add(t.left);
                queue.add(t.right);
            }

            if (arr.size() != 0)
                ret.add(arr);
        }
        return ret;
    }


    static class TreeNode {
        Object data;
        TreeNode left;
        TreeNode right;

        public TreeNode() {
        }

        public TreeNode(Object data, TreeNode left, TreeNode right) {
            this.data = data;
            this.left = left;
            this.right = right;
        }
    }

    public static TreeNode arrayToBTree(Object[] arrs) {

        List<TreeNode> nodes = new ArrayList<>(arrs.length);
        for (Object obj : arrs) {
            TreeNode treeNode = new TreeNode();
            treeNode.data = obj;
            nodes.add(treeNode);
        }

        for (int i = 0; i < arrs.length/2 - 1; i++) {
            TreeNode node = nodes.get(i);
            node.left = nodes.get(i*2 + 1);
            node.right = nodes.get(i*2 + 2);
        }
        // 只有当总节点数是奇数时，最后一个父节点才有右子节点
        int lastPNodeIndex = arrs.length/2 - 1;
        TreeNode lastPNode = nodes.get(lastPNodeIndex);
        lastPNode.left = nodes.get(lastPNodeIndex*2 + 1);
        if (arrs.length%2 != 0) {
            lastPNode.right = nodes.get(lastPNodeIndex*2 + 2);
        }

        return nodes.get(0);
    }