lintcode:Binary Tree Serialization

Design an algorithm and write code to serialize and deserialize a binary tree. Writing the tree to a file is called ‘serialization’ and reading back from the file to reconstruct the exact same binary tree is ‘deserialization’.

There is no limit of how you deserialize or serialize a binary tree, you only need to make sure you can serialize a binary tree to a string and deserialize this string to the original structure.

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * This method will be invoked first, you should design your own algorithm 
     * to serialize a binary tree which denote by a root node to a string which
     * can be easily deserialized by your own "deserialize" method later.
     */
    void serializeHelper(TreeNode *node,string& res){
        if(node){
            res+=to_string(node->val)+" ";
        }else{
            res+="# ";
            return;
        }

        serializeHelper(node->left,res);
        /*
        if(node->left){
            serializeHelper(node->left,res);
        }else{
            res+="# ";
        }*/

        serializeHelper(node->right,res);
        /*
        if(node->right){
            serializeHelper(node->right,res);
        }else{
            res+="# ";
        }*/
    }

    string serialize(TreeNode *root) {
        // write your code here

        string res="";

        serializeHelper(root,res);

        return res;
    }

    /**
     * This method will be invoked second, the argument data is what exactly
     * you serialized at method "serialize", that means the data is not given by
     * system, it's given by your own serialize method. So the format of data is
     * designed by yourself, and deserialize it here as you serialize it in 
     * "serialize" method.
     */
    TreeNode* deserializeHelper(istringstream& ss){
        string str;
        ss>>str;
        if(str[0]=='#'){
            return NULL;
        }

        int value=atoi(str.c_str());

        TreeNode *node=new TreeNode(value);

        node->left=deserializeHelper(ss);

        node->right=deserializeHelper(ss);

        return node;
    }

    TreeNode *deserialize(string data) {
        // write your code here

        istringstream ss(data);

        TreeNode *root=deserializeHelper(ss);

        return root;
    }
};