449. Serialize and Deserialize BST

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449. Serialize and Deserialize BST

Description

Serialization is 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 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.

Example 1:

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Input: root = [2,1,3]
Output: [2,1,3]

Example 2:

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Input: root = []
Output: []

Constraints:

  • The number of nodes in the tree is in the range [0, 10^4].
  • 0 <= Node.val <= 10^4
  • The input tree is guaranteed to be a binary search tree.

Hints/Notes

  • 2024/07/06
  • binary search tree
  • No solution from 0x3F

Solution

Language: C++

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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 {
public:
    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        if (!root) {
            return "";
        }
        string res = to_string(root->val);
        if (root->left) {
            res += "," + serialize(root->left);
        }
        if (root->right) {
            res += "," + serialize(root->right);
        }
        return res;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        if (data.empty()) {
            return nullptr;
        }
        vector<int> nums;
        int pos = 0;
        while ((pos = data.find(",")) != string::npos) {
            nums.push_back(stoi(data.substr(0, pos)));
            data.erase(0, pos + 1);
        }
        nums.push_back(stoi(data));
        return build(nums, 0, nums.size() - 1);
    }

    TreeNode* build(vector<int>& nums, int start, int end) {
        if (start > end) {
            return nullptr;
        }
        TreeNode* root = new TreeNode(nums[start]);
        if (start == end) {
            return root;
        }
        int i;
        for (i = start; i <= end && nums[i] <= root->val; i++) {
        }
        root->left = build(nums, start + 1, i - 1);
        root->right = build(nums, i, end);
        return root;
    }
};

// Your Codec object will be instantiated and called as such:
// Codec* ser = new Codec();
// Codec* deser = new Codec();
// string tree = ser->serialize(root);
// TreeNode* ans = deser->deserialize(tree);
// return ans;