297. 二叉树的序列化与反序列化

public class Codec {
    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        return String.join(",", serialize(root, new LinkedList<>()));
    }

    private List<String> serialize(TreeNode treeNode, List<String> valueList) {
        if (treeNode == null) {
            valueList.add("null");
        } else {
            valueList.add(String.valueOf(treeNode.val));
            serialize(treeNode.left, valueList);
            serialize(treeNode.right, valueList);
        }

        return valueList;
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        String[] values = data.split(",");
        List<String> valueList = new LinkedList<>(Arrays.asList(values));
        return deserialize(valueList);
    }

    private TreeNode deserialize(List<String> valueList) {
        if (valueList.get(0).equals("null")) {
            valueList.remove(0);
            return null;
        }

        TreeNode treeNode = new TreeNode(Integer.parseInt(valueList.get(0)));
        valueList.remove(0);
        treeNode.left = deserialize(valueList);
        treeNode.right = deserialize(valueList);
        return treeNode;
    }
}