Serialize and Deserialize Binary Tree

This page explains Java solution to problem Serialize and Deserialize Binary Tree using Pre-Order Traversal of binary tree data structure.

Problem Statement

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.

public String serialize(TreeNode root) should be able to convert TreeNode to String.
public TreeNode deserialize(String data) should be able to convert String to back to TreeNode format.

Solution

package com.vc.hard;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class SerializeAndDeserializeBinaryTree {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        StringBuilder sb = new StringBuilder();
        serialize(root, sb);
        return sb.toString();
    }

    private void serialize(TreeNode root, StringBuilder sb) {
        if(root == null) {
            sb.append("NULL ");
        }
        else {
            sb.append(root.val);
            sb.append(" ");
            serialize(root.left, sb);
            serialize(root.right, sb);
        }
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Queue<String> q = new LinkedList<>(Arrays.asList(data.split(" ")));
        return deserializeList(q);
    }

    private TreeNode deserializeList(Queue<String> q) {
        if(q.isEmpty()) return null;

        String element = q.peek();

        if(element.equals("NULL")) {
            q.poll();
            return null;
        }
        else {
            int value = Integer.parseInt(element);
            q.poll();
            TreeNode root = new TreeNode(value);
            root.left = deserializeList(q);
            root.right = deserializeList(q);
            return root;
        }
    }
}

Time Complexity

O(N) Where
N is total number of elements in an input tree.

Space Complexity

O(N) Where
N is total number of elements in an input tree.