【剑指Offer】【树】序列化二叉树

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};
*/
class Solution {
public:
    //序列化
    void do_Serialize(TreeNode *root, string &s)
    {
        if(root == nullptr)
        {
            s += ‘#‘;
            s += ‘,‘;
            return;
        }
        //std::to_string() 数值转换字符串
        s += to_string(root->val);
        s += ‘,‘;
        do_Serialize(root->left,s);
        do_Serialize(root->right,s);
    }
    char* Serialize(TreeNode *root) 
    {    
        if(root == nullptr)
        {
            return nullptr;
        }
        string str = "";
        do_Serialize(root,str);
        //返回值是char *
        char *ret = new char[str.length() + 1]; //‘\0‘
        strcpy(ret, str.c_str());
        return ret;
    }
    
    //反序列化
    TreeNode* do_Deserialize(string &s)
    {
        if(s.empty())
        {
            return nullptr;
        }
        if (s[0] == ‘#‘)
        {
            s = s.substr(2);    //从s中去掉#,
            return nullptr;
        }
        TreeNode *ret = new TreeNode(stoi(s));
        
        s = s.substr(s.find_first_of(‘,‘) + 1);
        
        ret->left = do_Deserialize(s);
        ret->right = do_Deserialize(s);
        return ret;
    }
    TreeNode* Deserialize(char *str) 
    {
        if(str == nullptr)
        {
            return nullptr;
        }
        string s(str);
        return do_Deserialize(s);
    }
};