Serialize and Deserialize Binary Tree

Description

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

Solution

/**
 * 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) {
        string ret;
        serializeHelper(root, ret);
        cout << ret << endl;
        return ret;
    }
    
    void serializeHelper(TreeNode* root, string& ret) {
        if (root == NULL) {ret += '#'; return;}
        ret += to_string(root->val);
        ret += ',';
        serializeHelper(root->left, ret);
        serializeHelper(root->right, ret);
        return;   
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        int index = 0;
        TreeNode* ret = deserializeHelper(data, index);
        return ret;
    }
    
    TreeNode* deserializeHelper(string& data, int& index) {
        if (index == data.size() || data[index] == '#') {
            ++index;
            return NULL;
        }
        int number = extractNumber(data, index);
        TreeNode* ret = new TreeNode(number);
        
        index += 1; //Skip the ','
        ret->left = deserializeHelper(data, index);
        ret->right = deserializeHelper(data, index);
        cout << number << " ";
        cout << index << endl;
        return ret;
    }
    
    int extractNumber(string& data, int& index) {
        int ret = 0;
        int sign = 1;
        if (data[index] == '-') {sign = -1; ++index; }
        while ('0'<=data[index] && '9'>=data[index]) {ret = ret * 10 + data[index] - '0'; ++index;}
        
        return ret * sign;
    }
};

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