Serialize a tree，最容易的還是前序遍歷，用空格分開節點即可。

Deserialize 也很容易，遞迴即可。

/**
 * 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 "#";
        return to_string(root->val)+' '+serialize(root->left)+' '+serialize(root->right);
    }
    

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string
 
 data) {
        return dfs(data);
    }
    
    TreeNode* dfs(string &data){
        if (data[0]=='#'){
            if (data.size()>2)
                data = data.substr(2);
            return NULL;
        }else{
            int pos=data.find(' ');
            TreeNode *node=new TreeNode(stoi(data.substr(0
 
,pos)));
            data = data.substr(pos+1);
            node->left = dfs(data);
            node->right = dfs(data);
            return node;
        }
    }
};

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

Follow up:

如果node不是數字而是任意字串怎麼辦。

可以借鑑TCP的思想，每個字串前先記錄字串的個數，如 2#ab 之類的即可。