二叉樹的序列化與反序列化(Serialize and Deserialize Binary Tree)

二叉樹的序列化與反序列化

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.

Example:

You may serialize the following tree:

    1
   / \
  2   3
     / \
    4   5

as "[1,2,3,null,null,4,5]"

Clarification: The above format is the same as how LeetCode 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.

思路與代碼

Codec

public class Codec {

    //序列化
    public String serialize(TreeNode root) {      //用StringBuilder
        StringBuilder res = ser_help(root, new StringBuilder());
        return res.toString();
    }
    
    public StringBuilder ser_help(TreeNode root, StringBuilder str){
        if(null == root){
            str.append("null,");
            return str;
        }
        str.append(root.val); 
        str.append(",");
        str = ser_help(root.left, str);
        str = ser_help(root.right, str);
        return str;
    }

    //反序列化
    public TreeNode deserialize(String data) {
        String[] str_word = data.split(",");
        List<String> list_word = new LinkedList<String>(Arrays.asList(str_word));
        return deser_help(list_word);
    }
    
    public TreeNode deser_help(List<String> li){
        if(li.get(0).equals("null")){
            li.remove(0);
            return null;
        }
        TreeNode res = new TreeNode(Integer.valueOf(li.get(0)));
        li.remove(0);
        res.left = deser_help(li);
        res.right = deser_help(li);
        return res;
    }
}

TreeNode

/** Definition for a binary tree node. */
public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

test

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