/**
 * 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) {
        StringBuilder sb = new StringBuilder();
        seHelper(root, sb);
        return sb.toString();
    }

    private void seHelper(TreeNode root, StringBuilder sb) {
        if(root == null) {
            sb.append("n,");
            return;
        }
        sb.append(String.valueOf(root.val) + ",");
        seHelper(root.left, sb);
        seHelper(root.right, sb);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        String[] parts = data.split(",");
        int[] d = new int[1];
        return deHelper(parts, d);
    }

    private TreeNode deHelper(String[] parts, int[] d) {
        if(parts[d[0]].equals("n")) {
            d[0]++;
            return null;
        }
        TreeNode root = new TreeNode(Integer.valueOf(parts[d[0]]));
        d[0]++;
        root.left = deHelper(parts, d);
        root.right = deHelper(parts, d);
        return root;
    }
}