Implements two functions for serializing and deserializing binary trees.

Serialize a binary tree. Given a binary tree, traverse it in some way. The empty child node is represented by '#', and the numbers are separated by commas.

such as

The results of serialization are: 1, 2, 4, 3, 5, 6##

In the process of serialization, the preorder traversal method of binary tree can be considered for serialization.

    //Convert int data to str
    string to_string(int val)
    {
        string res="";
        while(val)
        {
            int num=val%10;
            char temp=num+48;
            res+=temp;
            val/=10;
        }
        reverse(res.begin(),res.end());
        return res;
    }
    
    string str="";
    
    //Serialize main function
    void S_core(TreeNode *root,string &str)
    {
        if(root==NULL)
        {
            str+='#';
            return;
        }
        
        else
        {
            str+=to_string(root->val);
            str+=',';
            S_core(root->left,str);
            S_core(root->right,str);
        }
    }
    
    //Serialization function
    char* Serialize(TreeNode *root) {    
        if(root==NULL)
            return NULL;

        S_core(root,str);
        char *s=new char[str.size()+1];
        for(int i=0;i<str.size();i++)
        {
            s[i]=str[i];
        }
        s[str.size()]='\0';
        return s;
    }

The deserialization corresponding to serialization also adopts the way of preorder traversal.

Note that the parameter of the d'u core function is a reference, which can also be used as a secondary pointer.

    //Deserialize main function
    TreeNode* D_core(char* &str)
    {
        if(*str=='#')
        {
            str++;
            return NULL;
        }
        
        int num=0;
        while(*str!=','&&*str!='\0')
        {
            num=num*10+*str-'0';
            str++;
        }
        
        TreeNode *root=new TreeNode(num);
        if(*str=='\0')
            return root;
        else
            str++;
        root->left=D_core(str);
        root->right=D_core(str);
        
        return root;
    }
    
    //Deserialization function
    TreeNode* Deserialize(char *str) {
        if(str==NULL)
            return NULL;
        else
            return D_core(str);
    }