【剑指offer】序列化二叉树

public class  {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;
    
    public (int val) {
        this.val = val;
    }
}

private int idx = -1;

public String Serialize(TreeNode root) {
    StringBuilder sb = new StringBuilder();

    if (root == null) {
        sb.append("$,");
        return sb.toString();
    }

    sb.append(root.val).append(",");
    sb.append(Serialize(root.left));
    sb.append(Serialize(root.right));

    return sb.toString();
}

public TreeNode Deserialize(String str) {
    if (str == null || str.length() < 1)
        return null;

    String[] strs = str.split(",");

    return Deserialize(strs);
}

private TreeNode Deserialize(String[] strs) {
    idx++;
    TreeNode root = null;

    if (idx < strs.length && !strs[idx].equals("$")) {
        root = new TreeNode(Integer.valueOf(strs[idx]));
        root.left = Deserialize(strs);
        root.right = Deserialize(strs);
    }

    return root;
}