449. Serialize and Deserialize BST

• Difficulty: Medium

• Topics: Tree

• Similar Questions:

  • Serialize and Deserialize Binary Tree

  • Find Duplicate Subtrees

  • Serialize and Deserialize N-ary Tree

Problem:

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.

Solutions:

/**
 * 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) {
        string s;
        serializeHelper(root, s);
        return s;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        int pos = 0;
        return deserializeHelper(data, pos, INT_MAX);
    }

    TreeNode* deserializeHelper(string& data, int& pos, int upper) {
        if (pos * sizeof(int) == data.length())   return NULL;
        int val = *((reinterpret_cast<int*> (data.data())) + pos); // data.data()!
        if (val > upper)   return NULL;
        TreeNode* root = new TreeNode(val);
        pos += 1;
        root->left = deserializeHelper(data, pos, val - 1);
        root->right = deserializeHelper(data, pos, upper);
        return root;
    }

    void serializeHelper(TreeNode* root, string& s) {
        if (root == NULL)   return;
        s.append(reinterpret_cast<const char*>(&root->val), sizeof(root->val));
        serializeHelper(root->left, s);
        serializeHelper(root->right, s);
    }
};

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