Serialize and Deserialize Binary Tree

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.

For example, you may serialize the following tree

    1
   / \
  2   3
     / \
    4   5

as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

Credits:
Special thanks to @Louis1992 for adding this problem and creating all test cases.

• the format of serialized code looks as follows
  • rootnode(serialized_root->left, serialized_root->right)

/**
 * 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 ans;
        if(root == nullptr) return "";
        ans.append(to_string(root->val));
        ans.push_back('(');
        ans.append(serialize(root->left));
        ans.push_back(',');
        ans.append(serialize(root->right));
        ans.push_back(')');
        return ans;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        return _deserialize(data);
    }
    TreeNode* _deserialize(string& data) {
        if(data.size() == 0 || data[0] == '(' || data[0] == ')' || data[0] == ',') return nullptr;
        TreeNode * root = new TreeNode(parseNum(data));
        data.erase(0, 1); // erase '('
        root->left = _deserialize(data);
        data.erase(0, 1); // erase ','
        root->right = _deserialize(data);
        data.erase(0, 1); // erase ')'
        return root;
    }
    int parseNum(string & data){
        int ans = 0;
        int flag = 1;
        int i = 0;
        if(data[0] == '-'){
            flag = -1;
            i = 1;
        }
        while(data[i] <= '9' && data[i] >= '0'){
            ans = ans * 10 + data[i] - '0';
            i++;
        }
        ans = ans * flag;
        data.erase(0, i);
        return ans;
    }
};

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