binarySearchTree.js

/**
 * Definition for binary tree
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */

/**
 * @constructor
 * @param {TreeNode} root - root of the binary search tree
 */

var BSTIterator = function(root) {
    this.stack = [];
    while(root) {
        this.stack.push(root);
        root = root.left;
    }
};

BSTIterator.prototype.hasNext = function() {
    return this.stack.length != 0;
};

BSTIterator.prototype.next = function() {
    let subTreeRoot = this.stack.pop();
    let nextVal = subTreeRoot.val;
    
    subTreeRoot = subTreeRoot.right;
    while(subTreeRoot) {
        this.stack.push(subTreeRoot);
        subTreeRoot = subTreeRoot.left;
    }
    
    return nextVal;
};

/*
 * Your BSTIterator will be called like this:
 * var i = new BSTIterator(root), a = [];
 * while (i.hasNext()) a.push(i.next());
*/