[LeetCode]Serialize and Deserialize Binary Tree
题目链接:Serialize and Deserialize Binary Tree
题目内容:
Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.
Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.
For example, you may serialize the following tree
1 / \ 2 3 / \ 4 5as
"[1,2,3,null,null,4,5]"
,
just the same as how LeetCode OJ serializes
a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.
Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
题目要求对一个用TreeNode链表存储的二叉树进行序列化与反序列化,最后得到原始的TreeNode链表则说明成功。
因为题目并不关心中间过程得到的序列化串,因此不必拘泥于LeetCode常用的表示法,而可以使用自己的表示法。
为了方便重建,我们使用前序遍历,并且每当碰到一个NULL孩子,就存储一个#字符。
这样来说,在存储题目给出的树的时候,我们会得到[1,2,#,#,3,4,#,#,5,#,#,]这么一个字符串。
在还原时,只需要按照前序遍历的方式递归着解析这个序列化串,使用的核心方法为字符串的substr、find方法,该方法常用的形式有两种:①str.substr(location),这个方法会返回str从location开始到结尾的字串。②str.substr(location,len),这个方法会返回[location,location+len)区间的字符串,注意右面为开区间。str.find(charset)将返回str中第一个匹配到的charset的位置。
【具体实现】
为了方便递归,我们定义两个类的私有方法。
1.序列化
按照前序遍历的规则访问root,对于root为NULL的情况拼接#,其他情况拼接结点的数字,为了实现数字到字符串的转换,使用stringstream。
2.反序列化
递归函数的参数为(TreeNode *&root, string &data),根据data分割出的值val来决定root的值,如果val是#,则说明这是一个空结点,直接令root=NULL,否则创建一个新的TreeNode作为root,注意解析val值使用的是C函数atoi,需要用字符串的c_str()方法得到char*字符串,继续递归root的左右儿子,注意此时传入的data是已经去掉处理完部分的字串。反序列化的递归顺序与前序遍历保持一致。
代码如下:
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Codec { public: // Encodes a tree to a single string. string serialize(TreeNode* root) { string res; preOrderSerialize(root,res); cout << res; return res; } // Decodes your encoded data to tree. TreeNode* deserialize(string data) { TreeNode *root = NULL; preOrderDeserialize(root,data); return root; } private: void preOrderSerialize(TreeNode *root, string &str){ if(!root){ str += "#,"; return; } stringstream ss; ss << root->val; str += ss.str(); str += ","; preOrderSerialize(root->left,str); preOrderSerialize(root->right,str); } void preOrderDeserialize(TreeNode *&root, string &data){ if(data.length() == 0) return; string tmp = data.substr(0,data.find(',')); data = data.substr(data.find(',')+1); if(tmp.compare("#") == 0) root = NULL; else{ root = new TreeNode(atoi(tmp.c_str())); preOrderDeserialize(root->left,data); preOrderDeserialize(root->right,data); } } }; // Your Codec object will be instantiated and called as such: // Codec codec; // codec.deserialize(codec.serialize(root));