1 /** 2  * Definition for a binary tree node. 3  * public class TreeNode { 4  *     int val; 5  *     TreeNode left; 6  *     TreeNode right; 7  *     TreeNode(int x) { val = x; } 8  * } 9  */10 public class Codec {11 12     // Encodes a tree to a single string.13     public String serialize(TreeNode root) {14         if (root == null) {15             return null;16         }17         StringBuilder result = new StringBuilder();18         dfs(root, result);19         return result.toString();20     }21     22     private void dfs(TreeNode root, StringBuilder sb) {23         if (root == null) {24             sb.append(" ").append("#");25             return;26         }27         sb.append(root.val).append("#");28         dfs(root.left, sb);29         dfs(root.right, sb);30     }31 32     // Decodes your encoded data to tree.33     public TreeNode deserialize(String data) {34         if (data == null) {35             return null;36         }37         LinkedList
     
       nodeList = new LinkedList<>();38         nodeList.addAll(Arrays.asList(data.split("#")));39         return getTree(nodeList);40     }41     42     private TreeNode getTree(LinkedList
      
        nodeList) {43         String current = nodeList.poll();44         if (current == null || current.equals(" ")) {45             return null;46         }47         48         TreeNode root = new TreeNode(Integer.valueOf(current));49         root.left = getTree(nodeList);50         root.right = getTree(nodeList);51         return root;52     }53 }54 55 // Your Codec object will be instantiated and called as such:56 // Codec codec = new Codec();57 // codec.deserialize(codec.serialize(root));