297.Serialize and Deserialize Binary Tree

1-

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {
    private static final String spliter = ",";
    private static final String NN = "X";
    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        StringBuilder sb = new StringBuilder();
        buildString(root, sb);
        return sb.toString();
    }

    private void buildString(TreeNode node, StringBuilder sb){
        if(node == null){
            sb.append(NN).append(spliter);
        }
        else{
            sb.append(node.val).append(spliter);
            buildString(node.left, sb);
            buildString(node.right, sb);
        }
    }
    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        Deque<String> queue = new ArrayDeque<>();
        queue.addAll(Arrays.asList(data.split(spliter)));
        return buildTree(queue);
    }
    private TreeNode buildTree(Deque<String> queue){
        String val = queue.remove();
        if(val.equals(NN))
            return null;
        else{
            TreeNode node = new TreeNode(Integer.parseInt(val));
            node.left = buildTree(queue);
            node.right = buildTree(queue);
            return node;
        }
    }
}

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

2-

public class Codec {
    public String serialize(TreeNode root) {
    if( root == null ) return "";

    StringBuilder sb = new StringBuilder();
    Queue<TreeNode> queue = new LinkedList<>();
    queue.add(root);

    while( !queue.isEmpty() ){

        TreeNode temp = queue.poll();
        if( temp == null ){
            sb.append(" null");
            continue;
        }
        else{
            sb.append(" ");
            sb.append(String.valueOf(temp.val));
        }

        queue.add(temp.left);
        queue.add(temp.right);
    }

    return sb.toString().trim();
}

// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
    if( data == null || data.length() <=0 ) return null;

    String[] strArray = data.split(" ");
    int count = 0;
    Queue<TreeNode> queue = new LinkedList<>();

    TreeNode result = new TreeNode(Integer.parseInt(strArray[0]));
    queue.add(result);
    count++;

    while( !queue.isEmpty() ){
        TreeNode temp = queue.poll();
        if( !strArray[count].equals("null") ){
            TreeNode left = new TreeNode(Integer.parseInt(strArray[count]));
            temp.left = left;
            queue.add(left);                
        }
        count++;
        if( !strArray[count].equals("null") ){
            TreeNode right = new TreeNode(Integer.parseInt(strArray[count]));
            temp.right = right;
            queue.add(right);                
        }
        count++;
    }
    return result;
}
}