序列化和反序列化 N 叉树

/*
 * 思路：
 * 使用Java Stream API来实现序列化和反序列化。
 * 我们将节点的值和子节点的数量序列化为字符串。
 * 反序列化时，使用Stream生成节点。
 */
 
// 树节点定义
class Node {
    public int val;
    public List<Node> children;
    public Node() {}
    public Node(int _val) {
        val = _val;
    }
    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
}
 
import java.util.stream.Collectors;
import java.util.stream.IntStream;
 
class Codec {
    // 序列化
    public String serialize(Node root) {
        if (root == null) return "";
        return serializeHelper(root).collect(Collectors.joining(" "));
    }
 
    // 辅助方法：前序遍历
    private Stream<String> serializeHelper(Node node) {
        if (node == null) return Stream.empty();
        Stream<String> current = Stream.of(String.valueOf(node.val), String.valueOf(node.children.size()));
        Stream<String> children = node.children.stream().flatMap(this::serializeHelper);
        return Stream.concat(current, children);
    }
 
    // 反序列化
    public Node deserialize(String data) {
        if (data.isEmpty()) return null;
        Iterator<String> it = Arrays.stream(data.split(" ")).iterator();
        return deserializeHelper(it);
    }
 
    // 辅助方法：重建树
    private Node deserializeHelper(Iterator<String> it) {
        int val = Integer.parseInt(it.next());
        int size = Integer.parseInt(it.next());
        Node node = new Node(val, new ArrayList<>());
        IntStream.range(0, size).forEach(i -> node.children.add(deserializeHelper(it)));
        return node;
    }
}