序列化二叉树

请实现两个函数，分别用来序列化和反序列化二叉树

public class Solution {
    int index=-1;
    public String Serialize(TreeNode root) {
        StringBuilder strb = new StringBuilder();
        if(root==null){
            strb.append("#,");
            return strb.toString();
        }
        strb.append(root.val);
        strb.append(",");
        strb.append(Serialize(root.left));
        strb.append(Serialize(root.right));
        return strb.toString();
        
    }

    public TreeNode Deserialize(String str) {
        index++;
        String stra[] = str.split(",");
        TreeNode node = null;
        if(!stra[index].equals("#")){
            node = new TreeNode(Integer.valueOf(stra[index]));
            node.left = Deserialize(str);
            node.right=Deserialize(str);
        }
        return node;
    }
}