你可以序列化如下的二叉树

   / \

     / \

为："[8, 12, 2, null, null, 6, 4, null, null, null, null]"

/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

string str;

// Encodes a tree to a single string.

string serialize(TreeNode* root) {

    if (root == NULL) {

        if (!str.empty()) {

            str += ',';

        }

        str += "NULL";

        return str;

    }

    if (!str.empty()) {

        str += ',';

    }

    str += to_string(root->val);

    serialize(root->left);

    serialize(root->right);

    //cout << "str = " << str<<endl;

    return str;

}

string ParseString( string& data, int& val)

{

    string ret;

    if (data[] == ',') {

        data = data.substr();

    }

    if (data.empty()) {

    //    assert(0);

        val = -;

        return "";

    }

    else if (data[] == 'N') {

        val = -;

        ret = data.substr();

    }

    else if (data[] >= '' || data[] <= '') {

        int idx = ;

        while (data[idx] != ',' && idx < data.size()) {

            idx++;

        }

        string numstr = data.substr(, idx );

        ret = data.substr(idx );

        val = atoi(numstr.c_str());

    }

    else {

        //assert(0);

    }

    if (ret[] == ',') {

        ret = ret.substr();

    }

    return ret;

}

//8,12,NULL,NULL,2,6,NULL,NULL,4,NULL,NULL

TreeNode* deserializeInner(string& data)

{

    if (data.empty() || data == "NULL")

        return NULL;

    if (data[] == ',') {

        data = data.substr();

    }

    int val = -;

    string nextStr = ParseString(data, val);

    data = nextStr;

    if (val == -) {

        return NULL;

    }

    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));

    memset(root, , sizeof(TreeNode));

    root->val = val;

    root->left = deserializeInner(data);

    root->right = deserializeInner(data);

    return root;

}

// Decodes your encoded data to tree.

TreeNode* deserialize(string data) {

    if (data.empty() ||data == "NULL")

        return NULL;

    //cout << data<<endl;

    int val = -;

    string nextStr = ParseString(data, val);

    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));

    memset(root, , sizeof(TreeNode));

    root->val = val;

    root->left = deserializeInner(nextStr);

    root->right = deserializeInner(nextStr);

    return root;

}

};