【LeetCode & 剑指offer刷题】树题11:37 序列化二叉树(297. Serialize and Deserialize Binary Tree)

【LeetCode & 剑指offer 刷题笔记】目录(持续更新中...)

297. Serialize and Deserialize Binary Tree

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 tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.
Example: 
You may serialize the following tree:
 
     1
    / \
   2   3
       / \
       4  5
 
as "[1,2,3,null,null,4,5]"
Clarification: Just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.
Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
 
 
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
/*
利用前序遍历方式 序列化与反序列化
由于有表示空结点的符号存在,故可以唯一确定二叉树,而不需要与中序遍历序列相结合
*/
#include <string>
#include <sstream>
class Codec
{
public:
    // Encodes a tree to a single string.
    string serialize(TreeNode* root)
    {
        ostringstream out//构造字符串流
        seri(root, out);
        return out.str(); //out变为字符串返回
    }
    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data)
    {
        istringstream in(data); //构造字符串流
        return deseri(in);
    }
private:
    //序列化,树 -> 序列
    void seri(TreeNode *root, ostringstream &out)
    {
        if (root)
        {
            out << root->val << ' '; //处理根结点,用空格分隔(把序列当做树序列化时输出的容器),联系cout,将变量输出到cout
            seri(root->left, out); //递归左子树
            seri(root->right, out); //递归右子树
        }
        else //空结点时,置为'# '(注意#号后有空格)
        {
            out << "# ";
        }
    }
   
    //反序列化,序列 ->
    TreeNode* deseri(istringstream &in)
    {
        string val;   //有可能数字为多位数,故不能设定为char
        in >> val;    //反序列化,将序列中的值读出,联系cin,将输入值传给变量(分隔符为空格,可以直接用,若用其他分隔,可用getline函数)
      
        if (val == "#")
            return nullptr;
        else
        {
            TreeNode *root = new TreeNode(stoi(val)); //处理根结点
            root->left = deseri(in);   //递归左子树
            root->right = deseri(in);  //递归右子树
            return root;           
        }
    }
};
// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));
 
 
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
//掌握
//利用前序遍历方式 序列化与反序列化
//由于有表示空结点的符号存在,故可以唯一确定二叉树,而不需要与中序遍历序列相结合
#include <string>
#include <sstream>
class Codec
{
public:
    // Encodes a tree to a single string.
    string serialize(TreeNode* root)
    {
        if(root == nullptr) return "#";
        return to_string(root->val) + ',' + serialize(root->left) + ',' + serialize(root->right);
    }
    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data)
    {
        if(data == "#") return nullptr;
        stringstream s(data); //构造字符串流
        return deseri(s);
    }
private:
  /*  void seri(TreeNode* root, string& result)
    {
        if(root == nullptr)
        {
            result.push_back("#,"); //#表示空指针
            return;
        }
       
        result.push_back(to_string(root->val) + ','); //,为分隔符
        seri(root->left, result);
        seri(root->right, result);
    }*/
   
    TreeNode* deseri(stringstream& s)
    {
        string str; //有可能数字为多位数,故不能设定为char
        getline(s, str, ','); //getline 从输入流读取字符并将它们放进 string,默认分隔符是换行符,这里设置为分隔符为, (用getline可以逐步读取流中字符串,操作方便,相当于string容器每次访问后pop,流中字符会越来越少)
        if(str == "#") return nullptr;
        else
        {
            TreeNode* root = new TreeNode(stoi(str)); //stoi函数将整数转为字符串
            root->left = deseri(s);
            root->right = deseri(s);
            return root;
        }
       
    }
};
// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));
 
 

 

posted @ 2019-01-05 19:47  wikiwen  阅读(292)  评论(0编辑  收藏