449 Serialize and Deserialize BST 序列化和反序列化二叉搜索树

详见：https://leetcode.com/problems/serialize-and-deserialize-bst/description/

C++：

/**
 * 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 os;
        serializeHelper(root,os);
        return os.str();
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        istringstream is(data);
        return deserializeHelper(is);
    }
    void serializeHelper(TreeNode* root,ostringstream &os)
    {
        if(!root)
        {
            os<<"# ";
        }
        else
        {
            os<<root->val<<" ";
            serializeHelper(root->left,os);
            serializeHelper(root->right,os);
        }
    }
    TreeNode* deserializeHelper(istringstream &is)
    {
        string val;
        is>>val;
        if(val=="#")
        {
            return nullptr;
        }
        TreeNode* node=new TreeNode(stoi(val));
        node->left=deserializeHelper(is);
        node->right=deserializeHelper(is);
        return node;
    }
};

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

参考：https://www.cnblogs.com/grandyang/p/6224510.html