Leetcode[day20] - Construct Binary Search Tree from Preorder Traversal

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. Also recall that a preorder traversal displays the value of the node first, then traverses node.left, then traverses node.right.) It's guaranteed that for the given test cases there is al..