Serialize and Deserialize Binary Tree

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.

For example, you may serialize the following tree

    1
   / \
  2   3
     / \
    4   5

as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

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

Tips:

just use comma and null, BFS, O(n)

Code:

public String serialize(TreeNode root) {
    if (root == null) {
        return "null";
    }
    Queue<TreeNode> queue = new LinkedList<>();
    queue.add(root);
    StringBuilder result = new StringBuilder();
    while (!queue.isEmpty()) {
        int size = queue.size();
        for (int i = 0; i < size; i++) {
            TreeNode current = queue.poll();
            if (current == null) {
                result.append("null,");
                continue;
            }
            result.append(current.val).append(",");
            queue.offer(current.left);
            queue.offer(current.right);
        }
    }
    System.out.println(result);
    return result.toString();
}

// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
    String[] nodes = data.split(",");
    int index = 0;
    if (nodes[index].equals("null")) {
        return null;
    }
    TreeNode root = new TreeNode(Integer.parseInt(nodes[index++]));
    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);
    while (!queue.isEmpty()) {
        int size = queue.size();
        for (int i = 0; i < size; i++) {
            TreeNode current = queue.poll();
            if (!nodes[index].equals("null")) {
                current.left = new TreeNode(Integer.parseInt(nodes[index]));
                queue.offer(current.left);
            }
            index++;
            if (!nodes[index].equals("null")) {
                current.right = new TreeNode(Integer.parseInt(nodes[index]));
                queue.offer(current.right);
            }            
            index++;                
        }
    }
    return root;
}