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.

Solution:

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

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) {
            return null;
        }
        
        StringBuilder sb = new StringBuilder();
        Queue queue = new LinkedList();
        queue.add(root);
        
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node == null) {
                sb.append("null,");
            } else {
                sb.append(node.val + ",");
                queue.add(node.left);
                queue.add(node.right);
            }
        }
        
        return sb.toString();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data == null || data.length() == 0) {
            return null;
        } 
        
        String[] vals = data.split(",");
        if (vals[0] == "null") {
            return null;
        }
        
        TreeNode root = new TreeNode(Integer.parseInt(vals[0]));
        Queue queue = new LinkedList();
        queue.add(root);
        
        for (int i = 1; i < vals.length; i = i + 2) {
            TreeNode node = queue.poll();
            if (!vals[i].equals("null")) {
                TreeNode n = new TreeNode(Integer.parseInt(vals[i]));
                queue.add(n);
                node.left = n;
            }
            
            if (!vals[i + 1].equals("null")) {
                TreeNode n = new TreeNode(Integer.parseInt(vals[i + 1]));
                queue.add(n);
                node.right = n;
            }
        }
        
        return root;
    }
}

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