[leetcode]297. Serialize and Deserialize Binary Tree

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本文介绍了一种二叉树的序列化与反序列化的算法实现，通过两个方法将二叉树转化为字符串形式，并能从字符串中恢复原始的二叉树结构。提供了两种不同的实现方式，包括递归前序遍历的方法。

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题目链接：https://leetcode.com/problems/serialize-and-deserialize-binary-tree/description/

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.

For example, you may serialize the following tree

as "[1,2,3,null,null,4,5]" , 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.

Credits:
Special thanks to @Louis1992 for adding this problem and creating all test cases.

方法一：

class Codec{
public:
    string serialize(TreeNode* root)
    {
        if (!root) return " #";
        string res=" "+to_string(root->val);
        return res+serialize(root->left)+serialize(root->right);
    }
    TreeNode* dfs(istringstream &is)
    {
        string str;
        is>>str;
        if(str=="#") return NULL;
        TreeNode* root=new TreeNode(stoi(str));
        root->left=dfs(is);
        root->right=dfs(is);
        return root;
    }

    TreeNode* deserialize(string data)
    {
        istringstream is(data);
        return dfs(is);
    }
};

方法二：

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) {
        return mydeserialize(data);
    }
    TreeNode* mydeserialize(string& data) {
        if (data[0]=='#') {
            if(data.size() > 1) data = data.substr(2);
            return nullptr;
        } else {
            TreeNode* node = new TreeNode(helper(data));
            node->left = mydeserialize(data);
            node->right = mydeserialize(data);
            return node;
        }
    }
private:
    int helper(string& data) {
        int pos = data.find(',');
        int val = stoi(data.substr(0,pos));
        data = data.substr(pos+1);
        return val;
    }
};