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1 序列化与反序列化

二叉树的序列化与反序列化

1.1 实现思路

1. 方式一：前序遍历
   1. 通过前序遍历方式实现二叉树的序列化
   2. 将结果存入队列中
   3. 要注意空节点也要存null
2. 方式二：层序遍历
   1. 层序遍历也是用队列实现
   2. 注意从左到右，遇到空节点存null

1.2 代码实现

/*** 二叉树的序列化与反序列化** @author wen*/
public class SerializeAndReconstructTree {public static class Node {public int val;public Node left;public Node right;public Node(int val) {this.val = val;}}/*** 二叉树的序列化（前序遍历实现）** @param head 头节点* @return 返回一个队列*/public static Queue<String> preSerial(Node head) {Queue<String> queue = new LinkedList<>();pres(queue, head);return queue;}private static void pres(Queue<String> queue, Node head) {if (head == null) {queue.add(null);} else {queue.add(String.valueOf(head.val));pres(queue, head.left);pres(queue, head.right);}}/*** 二叉树的反序列化（前序遍历实现）** @param preQueue 存着二叉树序列化的队列* @return 返回，反序列化的二叉树头节点*/public static Node buildByPreQueue(Queue<String> preQueue) {if (preQueue == null || preQueue.isEmpty()) {return null;}return preBuild(preQueue);}private static Node preBuild(Queue<String> preQueue) {String val = preQueue.poll();if (val == null) {return null;}Node head = new Node(Integer.parseInt(val));head.left = preBuild(preQueue);head.right = preBuild(preQueue);return head;}/*** 二叉树序列化（层序遍历实现）** @param head 二叉树头节点* @return 返回序列化后的队列*/public static Queue<String> levelSerial(Node head) {Queue<String> ans = new LinkedList<>();if (head == null) {ans.add(null);} else {ans.add(String.valueOf(head.val));Queue<Node> help = new LinkedList<>();help.add(head);while (!help.isEmpty()) {Node cur = help.poll();if (cur.left != null) {ans.add(String.valueOf(cur.left.val));help.add(cur.left);} else {ans.add(null);}if (cur.right != null) {ans.add(String.valueOf(cur.right.val));help.add(cur.right);} else {ans.add(null);}}}return ans;}/*** 反序列化（层序遍历实现）** @param levelQueue 序列化存入的队列* @return 返回，反序列化的二叉树头节点*/public static Node buildByLevelQueue(Queue<String> levelQueue) {if (levelQueue == null || levelQueue.isEmpty()) {return null;}Node head = generateNode(levelQueue.poll());Queue<Node> queue = new LinkedList<>();if (head != null) {queue.add(head);}Node node = null;while (!queue.isEmpty()) {node = queue.poll();node.left = generateNode(levelQueue.poll());node.right = generateNode(levelQueue.poll());if (node.left != null) {queue.add(node.left);}if (node.right != null) {queue.add(node.right);}}return head;}private static Node generateNode(String val) {if (val == null) {return null;}return new Node(Integer.parseInt(val));}
}