题目描述

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.

样例

Example: 

You may serialize the following tree:

    1
   / \
  2   3
     / \
    4   5

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

算法1

(DFS) $O(n)$

先序遍历树，用ostringstream存储字符串，如果遇空node用“# ”表示。解码时用istringstream读出每个node的值，生成树。

时间复杂度

每个节点跑一遍，O（n）
空间O（n）

参考文献

C++ 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) {
        ostringstream out;
        serialize(root, out);
        return out.str();
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        istringstream in(data);
        return deserialize(in);
    }
private:
    void serialize(TreeNode*root , ostringstream& out)
    {
        if(!root) out<<"# ";
        else
        {
            out<<root->val<<" ";
            serialize(root->left,out);
            serialize(root->right,out);
        }
    }
    TreeNode *deserialize(istringstream& in)
    {
        string word;
        in>>word;
        if(word=="#") return nullptr;
        TreeNode *root=new TreeNode(stoi(word));
        root->left=deserialize(in);
        root->right=deserialize(in);
        return root;
    }
};

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