LintCode (7) Binary Tree Serialization

Design an algorithm and write code to serialize and deserialize a binary tree. Writing the tree to a file is called 'serialization' and reading back from the file to reconstruct the exact same binary tree is 'deserialization'.

There is no limit of how you deserialize or serialize a binary tree, you only need to make sure you can serialize a binary tree to a string and deserialize this string to the original structure.

Have you met this question in a real interview? 

Yes

Example

An example of testdata: Binary tree {3,9,20,#,#,15,7}, denote the following structure:

  3
 / \
9  20
  /  \
 15   7

Our data serialization use bfs traversal. This is just for when you got wrong answer and want to debug the input.

You can use other method to do serializaiton and deserialization.

binary tree有三种traversal: inorder ,preorder and postorder.只有preorder和postorder才能保存结构的信息。所以考虑pre order和post order. 但是还是有区别， postorder走的是自底向上的路线，而preorder走的是自顶向下的路线。 逻辑好理解程度， 或者说在deserialize的时候preorder比较容易些。 所以这道题算是写两遍preorder，考察地方也就是to_string和stringstream了。。。lol

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/** * Definition of TreeNode: * class TreeNode { * public: * int val; * TreeNode *left, *right; * TreeNode(int val) { * this->val = val; * this->left = this->right = NULL; * } * } */ class Solution { public: /** * This method will be invoked first, you should design your own algorithm * to serialize a binary tree which denote by a root node to a string which * can be easily deserialized by your own "deserialize" method later. */ string serialize(TreeNode *root) { // write your code here string result; serializeHelper(root, result); return result; } void serializeHelper(TreeNode *root, string& result){ if (!root){ result += "# "; return; } result= result+to_string(root->val)+" "; serializeHelper(root->left, result); serializeHelper(root->right, result); } /** * This method will be invoked second, the argument data is what exactly * you serialized at method "serialize", that means the data is not given by * system, it's given by your own serialize method. So the format of data is * designed by yourself, and deserialize it here as you serialize it in * "serialize" method. */ TreeNode *deserialize(string data) { // write your code here stringstream ss(data); return deserializeHelper(ss); } TreeNode* deserializeHelper(stringstream& ss){ string val; ss>>val; if (val=="#") return 0; int value=atoi(val.c_str()); TreeNode* root= new TreeNode(value); root->left=deserializeHelper(ss); root->right=deserializeHelper(ss); return root; } };