LeetCode 449. Serialize and Deserialize BST

原题网址：https://leetcode.com/problems/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.

方法：采用二进制数据格式进行序列化和反序列化。

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Codec {    private void code(TreeNode node, StringBuilder coded) {        if (node == null) return;        char flag = (char)0;        if (node.left != null) flag |= (char)1;        if (node.right != null) flag |= (char)2;        coded.append(flag);        for(int i = 0, val = node.val; i < 4; i++, val >>>= 8) {            coded.append((char)(val & 0xff));        }        code(node.left, coded);        code(node.right, coded);    }    private TreeNode decode(String data, int[] pos) {        if (pos[0] >= data.length()) return null;        char flag = data.charAt(pos[0]++);        int val = 0;        for(int i = 0; i < 4; i++) {            val |= (data.charAt(pos[0]++) << (i * 8));        }        TreeNode node = new TreeNode(val);        if ((flag & 1) != 0) {            node.left = decode(data, pos);        }        if ((flag & 2) != 0) {            node.right = decode(data, pos);        }        return node;    }    // Encodes a tree to a single string.    public String serialize(TreeNode root) {        if (root == null) return "";        StringBuilder coded = new StringBuilder();        code(root, coded);        return coded.toString();    }    // Decodes your encoded data to tree.    public TreeNode deserialize(String data) {        return decode(data, new int[] {0});    }}// Your Codec object will be instantiated and called as such:// Codec codec = new Codec();// codec.deserialize(codec.serialize(root));