297-Serialize-and-Deserialize-Binary-Tree.js

/**
 * 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) {
    const res = [];

    function dfs(node) {
        if (!node) {
            res.push('N');
            return;
        }

        res.push(String(node.val));
        dfs(node.left);
        dfs(node.right);
    }

    dfs(root);
    return res.join(',');
};

/**
 * Decodes your encoded data to tree.
 *
 * @param {string} data
 * @return {TreeNode}
 */
var deserialize = function (data) {
    const vals = data.split(',');
    let i = 0;

    function dfs() {
        if (vals[i] === 'N') {
            i++;
            return null;
        }

        const node = new TreeNode(parseInt(vals[i]));
        i++;
        node.left = dfs();
        node.right = dfs();
        return node;
    }

    return dfs();
};

/**
 * Your functions will be called as such:
 * deserialize(serialize(root));
 */