Serialize and Deserialize BST

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.

解析：

按先序遍历二叉树把每个节点地值存放在字符串中，解码时按对应的方式解码，由于要把数字存入字符串，每个数字之间使用分隔符。

在写的时候遇到很多问题，开始解码的函数使用的参数是(string s,int &pos)这样的形式，pos记录本次解码时s中起始位置，这个每次递归时

都要记录整个s字符串，会遇到内存溢出的问题，后来改进为(string &s)，其中每次递归时都对s进行处理，s只记录当前需要的位置。

代码：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Codec {
public:

    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        if (root==NULL) return "$ ";
        string ans=to_string(root->val)+" ";
        ans+=serialize(root->left);
        ans+=serialize(root->right);
        return ans;
      
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        int pos=0;
        return Derseial(data);
    }
    TreeNode* Derseial(string &data)
    {
      
        int pos=0;
       if (data[pos]=='$')
       {
           pos+=2;
           data=data.substr(pos,data.size()-pos);
           return NULL;
       }
      int endpos=data.size()-1;
       for (int i=pos; i<data.size(); i++)
       {
           if (data[i]==' ')
           {
               endpos=i;
               break;
           }
       }
       int value=atoi(data.substr(pos,endpos-pos).c_str());
       TreeNode *root=new TreeNode(value);
       //pos=endpos;
       data=data.substr(endpos+1,data.size()-endpos-1);
       root->left=Derseial(data);
       root->right=Derseial(data);
       return root;
    }
};

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