【LeetCode】297.Serialize and Deserialize Binary Tree(Hard)解题报告

【LeetCode】297.Serialize and Deserialize Binary Tree(Hard)解题报告

题目地址：https://leetcode.com/problems/serialize-and-deserialize-binary-tree/description/

题目描述：

  Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.

  Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.

For example, you may serialize the following tree

1
/ \
2   3
/ \
4   5
as "[1,2,3,null,null,4,5]", just the same as how LeetCode OJ serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

  Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

Solution:

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
非常非常重要，各大公司面经中经常出现
二叉树转成string，然后再转回二叉树
层序遍历
time : O(n)
space : O(n)
*/
public class Codec {

// Encodes a tree to a single string.
public String serialize(TreeNode root) {
if(root == null) return "";
StringBuilder res = new StringBuilder();
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while(!queue.isEmpty()){
TreeNode cur = queue.poll();
if(cur == null){
res.append("null ");
continue;
}
res.append(cur.val + " " );
queue.offer(cur.left);
queue.offer(cur.right);
}
return res.toString();
}

// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
if(data == "") return null;
String[] str = data.split(" ");
TreeNode root = new TreeNode(Integer.parseInt(str[0]));//根节点先提取出来
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
for(int i=1 ; i<str.length ; i++){
TreeNode cur = queue.poll();
if(!str[i].equals("null")){
cur.left = new TreeNode(Integer.parseInt(str[i]));
queue.offer(cur.left);
}
//不会越界
if(!str[++i].equals("null")){
cur.right = new TreeNode(Integer.parseInt(str[i]));
queue.offer(cur.right);
}
}
return root;
}
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));

Date：2018年3月22日