137 lines
3.0 KiB
Markdown
137 lines
3.0 KiB
Markdown
---
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id: 5cc0c1b32479e176caf3b422
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title: Check if Tree is Binary Search Tree
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challengeType: 1
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forumTopicId: 301624
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dashedName: check-if-tree-is-binary-search-tree
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---
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# --description--
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Since you already know what a binary search tree is, this challenge will establish how it is you can tell that a tree is a binary search tree or not.
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The main distinction of a binary search tree is that the nodes are ordered in an organized fashion. Nodes have at most 2 child nodes (placed to the right and/or left) based on if the child node's value is greater than or equal to (right) or less than (left) the parent node.
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# --instructions--
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In this challenge, you will create a utility for your tree. Write a JavaScript method `isBinarySearchTree` which takes a tree as an input and returns a boolean value for whether the tree is a binary search tree or not. Use recursion whenever possible.
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# --hints--
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Your Binary Search Tree should return true when checked with `isBinarySearchTree()`.
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```js
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assert(
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(function () {
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var test = false;
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if (typeof BinarySearchTree !== 'undefined') {
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test = new BinarySearchTree();
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} else {
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return false;
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}
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test.push(1);
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test.push(5);
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test.push(3);
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test.push(2);
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test.push(4);
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return isBinarySearchTree(test) == true;
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})()
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);
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```
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# --seed--
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## --after-user-code--
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```js
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BinarySearchTree.prototype.push = function(val) {
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var root = this.root;
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if (!root) {
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this.root = new Node(val);
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return;
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}
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var currentNode = root;
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var newNode = new Node(val);
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while (currentNode) {
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if (val < currentNode.value) {
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if (!currentNode.left) {
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currentNode.left = newNode;
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break;
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} else {
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currentNode = currentNode.left;
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}
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} else {
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if (!currentNode.right) {
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currentNode.right = newNode;
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break;
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} else {
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currentNode = currentNode.right;
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}
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}
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}
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};
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```
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## --seed-contents--
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```js
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var displayTree = (tree) => console.log(JSON.stringify(tree, null, 2));
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function Node(value) {
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this.value = value;
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this.left = null;
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this.right = null;
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}
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function BinarySearchTree() {
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this.root = null;
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}
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function isBinarySearchTree(tree) {
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// Only change code below this line
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// Only change code above this line
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}
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```
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# --solutions--
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```js
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var displayTree = (tree) => console.log(JSON.stringify(tree, null, 2));
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function Node(value) {
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this.value = value;
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this.left = null;
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this.right = null;
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}
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function BinarySearchTree() {
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this.root = null;
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}
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function isBinarySearchTree(tree) {
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if (tree.root == null) {
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return null;
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} else {
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let isBST = true;
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function checkTree(node) {
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if (node.left != null) {
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const left = node.left;
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if (left.value > node.value) {
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isBST = false;
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} else {
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checkTree(left);
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}
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}
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if (node.right != null) {
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const right = node.right;
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if (right.value < node.value) {
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isBST = false;
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} else {
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checkTree(right);
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}
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}
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}
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checkTree(tree.root);
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return isBST;
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}
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};
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```
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