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

   //50. 序列化二叉树
    // Encodes a tree to a single string.
    String serialize(TreeNode root) {
        if (root == null) {
            return "#";
        }
        return root.val + " " + serialize(root.left) + " " + serialize(root.right);
    }

    private String deserializeStr;


    // Decodes your encoded data to tree.
    TreeNode deserialize(String data) {
        deserializeStr = data;
        return deserialize();
    }

    private TreeNode deserialize() {
        if (deserializeStr.length() == 0) {
            return null;
        }
        int index = deserializeStr.indexOf(" ");
        String node  = index == -1 ? deserializeStr : deserializeStr.substring(0, index);
        deserializeStr = index == -1? "" : deserializeStr.substring(index + 1);
        if ("#".equals(node)) {
            return null;
        }
        int val = Integer.parseInt(node);
        TreeNode treeNode = new TreeNode(val);
        treeNode.left = deserialize();
        treeNode.right = deserialize();
        return treeNode;
    }
}