public String serialize(TreeNode root) {
    StringBuilder str = new StringBuilder();
    mySeri(root, str);
    return str.toString();
}


public TreeNode deserialize(String data) {
    List<String> list = new LinkedList<>(Arrays.asList(data.split(",")));
    return myDeSeri(list);
}





void mySeri(TreeNode root, StringBuilder sb) {
    if (root == null) {
        sb.append("null,");
        return;
    }

    sb.append(root.val + ",");
    mySeri(root.left, sb);
    mySeri(root.right, sb);
}



public TreeNode myDeSeri(List<String> list) {
    TreeNode root;
    String strValue = list.get(0);
    if ("null".equals(strValue)) {
        list.remove(0);
        return null;
    } else {
        int val = Integer.valueOf(strValue);
        root = new TreeNode(val);
        list.remove(0);
        // 当返回null的时候会结束
        root.left = myDeSeri(list);
        root.right = myDeSeri(list);
    }
    return root;
}


public TreeNode initTreeNode() {
    TreeNode treeNode4 = new TreeNode(4, null, null);
    TreeNode treeNode3 = new TreeNode(3, null, null);
    TreeNode treeNode2 = new TreeNode(2, treeNode3, treeNode4);

    TreeNode treeNode5 = new TreeNode(5, null, null);
    TreeNode root = new TreeNode(1, treeNode2, treeNode5);
    return root;
}

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }

    TreeNode(int x, TreeNode left, TreeNode right) {
        this.val = x;
        this.left = left;
        this.right = right;

    }
}

    @Test
    public void test() {
        System.out.println(serialize(initTreeNode()));
    }