序列化二叉树

题目：

请实现两个函数，分别用来序列化和反序列化二叉树

牛客网上通过的代码:

class Solution {
private:
    TreeNode* decode(char *&str) {
        if(*str=='#'){
            str++;
            return NULL;
        }
        int num = 0;
        while(*str != ',')
            num = num*10 + (*(str++)-'0');
        str++;
        TreeNode *root = new TreeNode(num);
        root->left = decode(str);
        root->right = decode(str);
        return root;
    }
public:
    char* Serialize(TreeNode *root) {   
        if(!root) return "#";
        string r = to_string(root->val);
        r.push_back(',');
        char *left = Serialize(root->left);
        char *right = Serialize(root->right);
        char *ret = new char[strlen(left) + strlen(right) + r.size()];
        strcpy(ret, r.c_str());
        strcat(ret, left);
        strcat(ret, right);
        return ret;
    }
    TreeNode* Deserialize(char *str) {
        return decode(str);
    }
};

《剑指offer》上的代码，更容易理解：

void Serialize( BinaryTreeNode* pRoot, ostream& stream )
{
    if ( pRoot == NULL )
    {
        stream << "$,";
        return ;
    }
    stream << pRoot->m_nvalue << ',';
    Serialize( pRoot->m_pLeft, stream );
    Serialize( pRoot->m_pRight, stream );
}

void Deserialize( BinaryTreeNode** pRoot, istream& stream )
{
    int number;
    if ( ReadStream( stream, &number ) )
    {
        *pRoot = new BinaryTreeNode();
        (*pRoot)->m_nvalue = number;
        (*pRoot)->m_pLeft = NULL;
        (*pRoot)->m_pRight = NULL;

        Deserialize( &((*pRoot)->m_pLeft), stream );
        Deserialize( &((*pRoot)->m_pRight), stream );
    }
}