Serialize and Deserialize BST

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 search tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.

The encoded string should be as compact as possible.

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

Solution: Preorder Traversal

Serialize and deserialize binary tree and binary serach tree is basically the same. We will use preorder traversal to encode and decode the tree.

class Codec {
public:
    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        ostringstream s;
        serializeUtil(root, s);
        return s.str();
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        istringstream s(data);
        return deserializeUtil(s);
    }

private:
    void serializeUtil(TreeNode* root, ostringstream &s) {
        if (!root) {
            s << ". ";
        } else {
            s << root->val << " ";
            serializeUtil(root->left, s);
            serializeUtil(root->right, s);
        }
    }

    TreeNode* deserializeUtil(istringstream &s) {
        string str = "";
        if (!(s >> str) || str == ".") return NULL;

        TreeNode *root = new TreeNode(stoi(str));
        root->left = deserializeUtil(s);
        root->right = deserializeUtil(s);
        return root;
    }
};