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 class Codec {

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) return "null";
        Queue<TreeNode> queue = new LinkedList<>();
        StringBuilder sb = new StringBuilder();
        queue.offer(root);
        while(!queue.isEmpty()) {
            TreeNode curt = queue.poll();
            if (curt == null) {
                sb.append("null ");
                continue;
            }
            sb.append(curt.val).append(" ");
            queue.offer(curt.left);
            queue.offer(curt.right);
        }
        return sb.toString().trim();
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        String[] nodes = data.split(" ");
        if (nodes[0].equals("null")) return null;
        TreeNode root = new TreeNode(Integer.valueOf(nodes[0]));
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        for (int i = 1; i < nodes.length; i++) {
            TreeNode curt = queue.poll();
            if (!nodes[i].equals("null")) {
                curt.left = new TreeNode(Integer.valueOf(nodes[i]));
                queue.offer(curt.left);
            }
            if (!nodes[++i].equals("null")) {
                curt.right = new TreeNode(Integer.valueOf(nodes[i]));
                queue.offer(curt.right);
            }
        }
        return root;
    }
}


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