[LeetCode] Serialize and Deserialize Binary Tree

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.

Credits:
Special thanks to @Louis1992 for adding this problem and creating all test cases.

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/**
 * 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 {
private:
    void _serialize(TreeNode *root, ostringstream &sout) {
        if (root == NULL) {
            sout << "# ";
            return;
        }
        sout << root->val << " ";
        _serialize(root->left, sout);
        _serialize(root->right, sout);
    }
    void _deserialize(TreeNode *&root, istringstream &sin) {
        int val;
        string tmp;
        if (sin >> tmp && tmp != "#") {
            val = stoi(tmp);
        } else {
            return;
        }
        root = new TreeNode(val);
        _deserialize(root->left, sin);
        _deserialize(root->right, sin);
    }
public:

    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        ostringstream sout;
        _serialize(root, sout);
        return sout.str();
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        istringstream sin(data);
        TreeNode *root = NULL;
        _deserialize(root, sin);
        return root;
    }
};

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