449. Serialize and Deserialize BST

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.

复杂度：

时间 O(N) 空间 O(N)

思路：

采用先序遍历的方式序列化，再采用同样的先序遍历反序列化。

/**
* 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) {
//base case
if(root == null)
return "$,";
//ensure
return root.val + "," + serialize(root.left) + serialize(root.right);
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
//require
Queue<String> q = new LinkedList<String>();
//convert to string[] by " "
String[] strs = data.split(",");
for(String str : strs){
q.add(str);
}
return dfs(q);
}
private TreeNode dfs(Queue<String> q){
String str = q.remove();
//base case
if(str.equals("$"))
return null;

TreeNode root = new TreeNode(Integer.valueOf(str));
root.left = dfs(q);
root.right = dfs(q);
//ensure
return root;
}
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(cod
4000
ec.serialize(root));