kth-smallest-element-in-a-bst.js

/**
 * Source:  https://leetcode.com/problems/kth-smallest-element-in-a-bst/
 * Tags:    [Tree,Binary Search]
 * Level:   Medium
 * Title:   Kth Smallest Element in a BST
 * Auther:  @imcoddy
 * Content: Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.
 *
 * Note:
 * You may assume k is always valid, 1 ≤ k ≤ BST's total elements.
 *
 * Follow up:
 * What if the BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How would you optimize the kthSmallest routine?
 *
 *
 *   Try to utilize the property of a BST.
 *   What if you could modify the BST node's structure?
 *   The optimal runtime complexity is O(height of BST).
 *
 *
 * Credits:Special thanks to @ts for adding this problem and creating all test cases.
 *
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 *                   Show Similar Problems
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 *                      (M) Binary Tree Inorder Traversal
 */

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} k
 * @return {number}
 */
var kthSmallest = function(root, k) {

};