LeetCode 449. Serialize and Deserialize BST

Question

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:

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

Example 2:

Input: root = []
Output: []

Solution

• Solution1 – preorder traversal

public class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) return "";
        String res = String.valueOf(root.val);
        if (root.left != null) res += "," + serialize(root.left);
        if (root.right != null) res += "," + serialize(root.right);
        return res;
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data.isEmpty()) return null;
        Queue<String> q = new LinkedList<>(Arrays.asList(data.split(",")));
        return deserialize(q, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }
    public TreeNode deserialize(Queue<String> q, int lower, int upper){
        if (q.isEmpty()) return null;
        String s = q.peek();
        int val = Integer.parseInt(s);
        if (val < lower || val > upper) return null;
        q.poll();
        TreeNode root = new TreeNode(val);
        root.left = deserialize(q, lower, val);
        root.right = deserialize(q, val, upper);
        return root;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(n)