二叉树的序列化和反序列化

import java.util.LinkedList;
import java.util.Queue;

/**
 * 序列化和反序列化二叉树
 * 先序、后序
 * (中序不能实现)
 * 按层
 */
public class SerializeAndReconstructTree {

    /**
     * 先序序列化
     *
     * @param head 头结点
     * @return 序列化结果
     */
    public Queue<String> preSerialize(Node head) {
        Queue<String> queue = new LinkedList<>();
        pres(head, queue);
        return queue;
    }

    private void pres(Node head, Queue<String> queue) {
        if (head == null) {
            queue.add(null);
        } else {
            queue.add(String.valueOf(head.value));
            pres(head.left, queue);
            pres(head.right, queue);
        }
    }

    /**
     * 先序反序列化
     *
     * @param queue 序列化队列
     * @return 二叉树
     */
    public Node buildByPreQueue(Queue<String> queue) {
        if (queue == null || queue.isEmpty()) {
            return null;
        }
        return preb(queue);
    }

    private Node preb(Queue<String> queue) {
        String value = queue.poll();
        if (value == null) {
            return null;
        }
        Node head = new Node(Integer.parseInt(value));
        head.left = preb(queue);
        head.right = preb(queue);
        return head;
    }

    /**
     * 按层序列化
     */
    public Queue<String> levelSerialize(Node head) {
        Queue<String> result = new LinkedList<>();
        if (head == null) {
            result.add(null);
            return result;
        }
        result.add(String.valueOf(head.value));
        Queue<Node> queue = new LinkedList<>();
        queue.add(head);
        while (!queue.isEmpty()) {
            Node node = queue.poll();
            if (node.left != null) {
                result.add(String.valueOf(node.left.value));
                queue.add(node.left);
            } else {
                result.add(null);
            }
            if (node.right != null) {
                result.add(String.valueOf(node.right.value));
                queue.add(node.right);
            } else {
                result.add(null);
            }
        }
        return result;
    }

    /**
     * 按层反序列化
     */
    public Node levelBuild(Queue<String> levelList) {
        if (levelList == null || levelList.isEmpty()) {
            return null;
        }
        Node head = generateNode(levelList.poll());
        Queue<Node> queue = new LinkedList<>();
        if (head != null) {
            queue.add(head);
        }
        Node node = null;
        while (!queue.isEmpty()) {
            node = queue.poll();
            node.left = generateNode(levelList.poll());
            if (node.left != null) {
                queue.add(node.left);
            }
            node.right = generateNode(levelList.poll());
            if (node.right != null) {
                queue.add(node.right);
            }
        }
        return head;
    }

    private Node generateNode(String value) {
        if (value == null) {
            return null;
        }
        return new Node(Integer.parseInt(value));
    }

    /**
     * 二叉树结构
     */
    public class Node {

        public int value;

        public Node left;

        public Node right;

        public Node(int value) {
            this.value = value;
        }

    }

}

/* 如有意见或建议，欢迎评论区留言；如发现代码有误，欢迎批评指正 */