LeetCode-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.

Credits:
Special thanks to @Louis1992 for adding this problem and creating all test cases.

Analysis:

While using bfs is intuitive, we can use dfs also.

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) {
        StringBuilder builder = new StringBuilder();
        serializeRecur(root,builder);
        return builder.toString();
    }

    public void serializeRecur(TreeNode cur, StringBuilder builder) {
        if (cur == null) {
            builder.append("n");
            return;
        }
        builder.append(cur.val);
        builder.append(" ");
        serializeRecur(cur.left,builder);
        builder.append(" ");
        serializeRecur(cur.right,builder);
    }

    int cur = -1;

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        cur = -1;
        String[] nodes = data.split(" ");
        return deseriazlieRecur(nodes);

    }

    public TreeNode deseriazlieRecur(String[] nodes) {
        cur++;
        if (nodes[cur].equals("n")) {
            return null;
        }

        TreeNode curNode = new TreeNode(Integer.parseInt(nodes[cur]));
        curNode.left = deseriazlieRecur(nodes);
        curNode.right = deseriazlieRecur(nodes);
        return curNode;
    }

}

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