Leetcode-449. Serialize and Deserialize BST

前言：为了后续的实习面试，开始疯狂刷题，非常欢迎志同道合的朋友一起交流。因为时间比较紧张，目前的规划是先过一遍，写出能想到的最优算法，第二遍再考虑最优或者较优的方法。如有错误欢迎指正。博主首发CSDN，mcf171专栏。

博客链接：mcf171的博客

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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.

这个题目可以结合BTS的特点，否则需要保存2n长度的树长度，才知道每一个位置在哪。Your runtime beats 19.61% of java submissions.

/** * 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) {      StringBuffer sb = new StringBuffer("");      Stack<TreeNode> stack = new Stack<TreeNode>();      stack.push(root);      while(stack.size() != 0){          root = stack.pop();          if(root != null){            stack.push(root.right);            stack.push(root.left);            sb.append(root.val);            sb.append(",");          }      }      return sb.toString();    }    // Decodes your encoded data to tree.    public TreeNode deserialize(String data) {        System.out.println(data);        if(data.length() == 0) return null;        String[] numbers = data.split(",");        TreeNode root = new TreeNode(Integer.parseInt(numbers[0]));        TreeNode iteratorNode = root;        Stack<TreeNode> stack = new Stack<TreeNode>();        for(int i = 1; i < numbers.length; i ++){            TreeNode node = new TreeNode(Integer.parseInt(numbers[i]));            if(node.val < iteratorNode.val) {iteratorNode.left = node;stack.push(iteratorNode);}            else {                while(!stack.empty()){                    TreeNode parentNode = stack.pop();                    if(node.val < parentNode.val) {iteratorNode.right = node;stack.push(parentNode);break;}                    else iteratorNode = parentNode;                }                if(stack.empty()) iteratorNode.right = node;            }            iteratorNode = node;        }                return root;    }}// Your Codec object will be instantiated and called as such:// Codec codec = new Codec();// codec.deserialize(codec.serialize(root));