* encoding-decoding.java

asd

Serialize-and-Deserialize.java

297. Serialize and Deserialize Binary Tree
https://leetcode.com/problems/serialize-and-deserialize-binary-tree/
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.
class solution {

    // Encodes a tree to a single string.
    private void buildString(TreeNode root, List<String> list) {
    	if(root==null) {
    		list.add("null");
    		return;
    	} 
	    list.add( String.valueOf( root.val ) );
	    buildString(root.left, list);
	    buildString(root.right, list);
    }	
	
    public String serialize(TreeNode root) {
    	List<String> list= new ArrayList<>();
    	buildString(root, list);
        return String.join(" ", list);
    }


    // Decodes your encoded data to tree.
    private TreeNode buildTree (Queue<String> nodes) {

    	String str= nodes.poll();
	    if( str.equals("null") ) return null;
	    
    	TreeNode node= new TreeNode( Integer.valueOf(str) );
    	node.left= buildTree(nodes);
    	node.right= buildTree(nodes);
    	return node;
   }
    
    public TreeNode deserialize(String data) {
    	Queue<String> nodes= new LinkedList<>( Arrays.asList(data.split(" ")) ); 
    	return buildTree(nodes);    	
    } 
}