/**
 * 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:

    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        string res;
        dfsEn(root, res);
        return res;
    }

    void dfsEn(TreeNode* node, string &res){
        if(!node){
            res+="#,";
            return;
        }
        res+=to_string(node->val)+",";
        dfsEn(node->left, res);
        dfsEn(node->right, res);
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        int pos=0;
        return dfsDe(data, pos);
    }

    TreeNode* dfsDe(string data, int& pos){
        if(data[pos]=='#'){
            pos+=2;
            return nullptr;
        }
        bool neg=false;
        if(data[pos]=='-'){neg=true; pos++;} 
        int v=0;
        while(data[pos]!=','){
            v=v*10+data[pos]-'0';
            pos++;
        }
        pos++;
        if(neg) v=-v;
        TreeNode *node = new TreeNode(v);
        node->left = dfsDe(data, pos);
        node->right = dfsDe(data, pos);
        return node;
    }
};