Added Binary Tree

README.md

@@ -42,6 +42,7 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 - [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
 
 - [Trees](src/_DataStructures_/Trees)
+  - [Binary Tree (creation using level order)](src/_DataStructures_/Trees/BinaryTree)
   - [Binary Search Tree](src/_DataStructures_/Trees/BinarySearchTree)
     - [Find k<sup>th</sup> maximum in a BinarySearchTree](src/_DataStructures_/Trees/BinarySearchTree/find-kth-max)
     - [Find k<sup>th</sup> minimum in a BinarySearchTree](src/_DataStructures_/Trees/BinarySearchTree/find-kth-min)

src/_DataStructures_/Trees/BinaryTree/Node.js

@@ -0,0 +1,7 @@
+module.exports = class Node {
+  constructor(value) {
+    this.value = value;
+    this.leftChild = null; // will be a node
+    this.rightChild = null; // will be a node
+  }
+};

src/_DataStructures_/Trees/BinaryTree/index.js

@@ -0,0 +1,51 @@
+const Node = require('./Node');
+
+class BinaryTree {
+  constructor(arr) {
+    if (!Array.isArray(arr) || !arr.length) {
+      throw new Error('Invalid argument to create a Binary Tre');
+    }
+    this.root = this.createBinaryTree((this.root = null), arr, 0);
+  }
+
+  // eslint-disable-next-line class-methods-use-this
+  createBinaryTree(root, arr, i) {
+    if (i < arr.length) {
+      // eslint-disable-next-line no-param-reassign
+      root = new Node(arr[i]);
+      // eslint-disable-next-line no-param-reassign
+      root.leftChild = this.createBinaryTree(root.leftChild, arr, 2 * i + 1);
+      // eslint-disable-next-line no-param-reassign
+      root.rightChild = this.createBinaryTree(root.rightChild, arr, 2 * i + 2);
+    }
+    return root;
+  }
+
+  traversePreorder(root) {
+    let arr = [];
+
+    if (root === null) return arr;
+    // push node to arr
+    arr.push(root.value);
+
+    // push left node
+    const left = this.traversePreorder(root.leftChild);
+    arr = [...arr, ...left];
+
+    // push right node
+    const right = this.traversePreorder(root.rightChild);
+    arr = [...arr, ...right];
+
+    return arr;
+  }
+
+  preOrder() {
+    return this.traversePreorder(this.root);
+  }
+}
+
+// const bt = new BinaryTree([1, 2, 3, 4, 5, 6]);
+// console.log(bt.root);
+// console.log(bt.preOrder());
+
+module.exports = BinaryTree;