Largest smaller binary search tree key - javascript

LargestSmallerBSTKey.js

/*********************************************************
 * CODE INSTRUCTIONS:                                    *
 * 1) The method findLargestSmallerKey you're            *
 *    asked to implement is located at line 26.          *
 * 2) Use the helper code below to implement it.         *
 * 3) In a nutshell, the helper code allows you to       *
 *    to build a Binary Search Tree.                     *
 * 4) Jump to line 71 to see an example for how the      *
 *    helper code is used to test findLargestSmallerKey. *
 *********************************************************/


// Constructor to create a new Node
function Node(key) {
  this.key = key;
  this.parent = null;
  this.left = null;
  this.right = null;
}

// Constructor to create a new BST 
function BinarySearchTree() {
  this.root = null;
}

BinarySearchTree.prototype.findLargestSmallerKey = function(num) {
  // your code goes here  
  
 var helper = function (node) {

    if(num <= node.key) {

      var left = node.left
      
      if(left == undefined) {
        return -1
      } 
      else 
      {
        return helper(node.left)
      }
    }
     
    if(num > node.key) 
    {      
      if(node.right == undefined) {                
        return node.key
      } 
      else 
      {
        return helper(node.right)
      }
    }
   
    return -1 
  }
 
  return helper(this.root)
}

// Creates a new node by a key and inserts it to the BST
BinarySearchTree.prototype.insert = function(key) {
  var root = this.root;

  // 1. If the tree is empty, create the root
  if(!root) {
      this.root = new Node(key);
      return;
  }

  // 2) Otherwise, create a node with the key
  //    and traverse down the tree to find where to
  //    to insert the new node
  var currentNode = root;
  var newNode = new Node(key);

  while(currentNode !== null) {
      if(key < currentNode.key) {
          if(!currentNode.left) {
              currentNode.left = newNode;
              newNode.parent = currentNode;
              break;
          } else {
              currentNode = currentNode.left;
          }
      } else {
          if(!currentNode.right) {
              currentNode.right = newNode;
              newNode.parent = currentNode;
              break;
          } else {
              currentNode = currentNode.right;
          }
      }
  }
}

/*********************************************
 * Driver program to test above function     *
 *********************************************/

// Create a Binary Search Tree
var bst = new BinarySearchTree();
bst.insert(20);
bst.insert(9);
bst.insert(25);
bst.insert(5);
bst.insert(12);
bst.insert(11);
bst.insert(14);

var result = bst.findLargestSmallerKey(17);

console.log("Largest smaller number is " + result);