[LeetCode][JavaScript]Serialize and Deserialize Binary Tree

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.

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.

https://leetcode.com/problems/serialize-and-deserialize-binary-tree/

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串行化和反串行化树。

串行化，中序遍历树，如果left或者right没有孩子，就用N代替，用#连接各个节点。

比图题中的例子，串行化之后是1#2#N#N#3#4#N#N#5#N#N。

反串行化还是中序遍历，递归建出树。

LDR方法有2个返回值，node是当前的节点对象，i是nodes下标。

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * Encodes a tree to a single string.
 *
 * @param {TreeNode} root
 * @return {string}
 */
var serialize = function(root) {
    var res = "";
    LDR(root);
    if(res[0] === '#'){
        res = res.substring(1);
    }
    return res;

    function LDR(node){
        if(node !== null && node.val !== undefined){
            res += "#" + node.val;
            if(node.left !== null){
                LDR(node.left);
            }else{
                res += "#N";
            }
            if(node.right !== null){
                LDR(node.right);
            }else{
                res += "#N";
            }
        }
    }
};

/**
 * Decodes your encoded data to tree.
 *
 * @param {string} data
 * @return {TreeNode}
 */
var deserialize = function(data) {
    var nodes = data.split('#');
    return LDR(0).node;

    function LDR(i){
        if(nodes[i] !== undefined && nodes[i] !== "" && nodes[i] !== 'N'){
            var root = new TreeNode(parseInt(nodes[i]));
            i++;
            var res = LDR(i);
            i = res.i;
            root.left = res.node;
            res = LDR(i);
            i = res.i;
            root.right = res.node;
            return {node : root, i : i};
        }else{
            return {node : null, i : ++i};
        }
    }
};