LeetCode 449. Serialize and Deserialize BST

原题链接在这里：https://leetcode.com/problems/serialize-and-deserialize-bst/description/

题目：

Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

Design an algorithm to serialize and deserialize a binary search tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.

The encoded string should be as compact as possible.

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

题解：

与Serialize and Deserialize Binary Tree相同解法.

Time Complexity: serialize, O(n). deserialize, O(n). Space: O(n).

AC Java:

 /**
  * 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();
         preorder(root, sb);
         return sb.toString();
     }

     private void preorder(TreeNode root, StringBuilder sb){
         if(root == null){
             sb.append("#").append(",");
             return;
         }
         sb.append(root.val).append(",");
         preorder(root.left, sb);
         preorder(root.right, sb);
     }

     // Decodes your encoded data to tree.
     public TreeNode deserialize(String data) {
         LinkedList<String> que = new LinkedList<String>();
         que.addAll(Arrays.asList(data.split(",")));
         return deserial(que);
     }

     private TreeNode deserial(LinkedList<String> que){
         String str = que.pollFirst();
         if(str.equals("#")){
             return null;
         }
         TreeNode root = new TreeNode(Integer.valueOf(str));
         root.left = deserial(que);
         root.right = deserial(que);
         return root;
     }
 }

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