/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) return "nil";
        StringBuilder sb = new StringBuilder();
        sb.append(Integer.toString(root.val));
        LinkedList<TreeNode> list = new LinkedList<>();
        list.add(root.left);
        list.add(root.right);
        while (list.size() != 0) {
            TreeNode node = list.poll();
            if (node == null) {
                sb.append(",nil");
            } else {
                sb.append(',');
                sb.append(Integer.toString(node.val));
                list.add(node.left);
                list.add(node.right);
            }
        }
        return sb.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data.equals("nil")) return null;
        String[] strs = data.split(",");
        TreeNode root = new TreeNode(Integer.parseInt(strs[0]));
        LinkedList<TreeNode> list = new LinkedList<>();
        list.add(root);
        for (int i = 1; i < strs.length; i++) {
            TreeNode node = list.poll();
            if (!strs[i].equals("nil")) {
                node.left = new TreeNode(Integer.parseInt(strs[i]));
                list.add(node.left);
            }
            if (!strs[++i].equals("nil")) {
                node.right = new TreeNode(Integer.parseInt(strs[i]));
                list.add(node.right);
            }
        }
        return root;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));