297. 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.

解题思路：将一棵树序列化和反序列化，规则自己制定。将树按先序遍历序列化之后，反序列化的时候的难点就是如何把那些数值重新拿出来。

/**
 * 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 "#";
        return to_string(root->val)+','+serialize(root->left)+','+serialize(root->right);
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        return mydeserialize(data);
    }
private:
    TreeNode* mydeserialize(string& data) {
        if(data[0] == '#') {
            if(data.length() > 1) data=data.substr(2);
            return NULL;
        } else {
            TreeNode* root = new TreeNode(helper(data));
            root->left = mydeserialize(data);
            root->right = mydeserialize(data);
            return root;
        } 
    }
    int helper(string& data){
        int pos = data.find(',');
        int val = stoi(data.substr(0,pos));
        data = data.substr(pos+1);
        return val;
    }
};

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