[leetcode] 297. Serialize and Deserialize Binary Tree 解题报告

题目链接:https://leetcode.com/problems/serialize-and-deserialize-binary-tree/

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   5

as

"[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.

思路：使用先根遍历来序列化二叉树，然后再递归的解码字符串．在C++中有提供一个很方便做字符串处理的类，istringstream．有了这个类你就可以不用手动分割字符串了，在序列化的时候每个结点的值之间留一个空格，他就可以一个个的按照空格分割的方式将字符串一个个吐出来．很方便有没有！

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) {
if(!root) return "#";
string str = to_string(root->val) + " ";
return str + " " + serialize(root->left) + " " + serialize(root->right);
}

// Decodes your encoded data to tree.
TreeNode* deserialize(string data) {
if(!flag) { is.str(data); flag=true; }
is >> str;
if(str == "#") return NULL;
TreeNode* root = new TreeNode(stoi(str));
root->left = deserialize(data);
root->right = deserialize(data);
return root;
}
private:
istringstream is;
bool flag = false;
string str;
};

// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));

参考:https://leetcode.com/discuss/76182/clean-c-solution
https://leetcode.com/discuss/66147/recursive-preorder-python-and-c-o-n