ConstructBinarySearchTreeFromPreorderTraversal.js

// Source : https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal
// Author : Dean Shi
// Date   : 2019-06-30

/***************************************************************************************
 *
 * Return the root node of a binary search tree that matches the given preorder
 * traversal.
 *
 * (Recall that a binary search tree is a binary tree where for every node, any
 * descendant of node.left has a value < node.val, and any descendant of node.right has
 * a value > node.val.  Also recall that a preorder traversal displays the value of the
 * node first, then traverses node.left, then traverses node.right.)
 *
 * Example 1:
 *
 * Input: [8,5,1,7,10,12]
 * Output: [8,5,10,1,7,null,12]
 *
 * Note:
 *
 * 1 <= preorder.length <= 100
 * The values of preorder are distinct.
 *
 ***************************************************************************************/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {number[]} preorder
 * @return {TreeNode}
 */
var bstFromPreorder = function(preorder) {
    if (!preorder.length) return null

    const [root, ...rest] = preorder

    const rootNode = new TreeNode(root)
    rootNode.left = bstFromPreorder(rest.filter(n => n < root))
    rootNode.right = bstFromPreorder(rest.filter(n => n > root))

    return rootNode
};