Merge pull request knaxus#49 from knaxus/problems

Added BST

Author: ashokdey

README.md

@@ -24,18 +24,21 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 
   - [Implement Queue Using Stack](src/_DataStructures_/Stack/immitate-queue-using-stack)
   - [Baseball Game](src/_DataStructures_/Stack/baseball-game)
-  - [Minimum Stack](src/_DataStructures_/Stack/min-stack)
+  - [Find minimum in the Stack](src/_DataStructures_/Stack/min-stack)
   - [Balanced Parenthesis](src/_DataStructures_/Stack/balanced-parenthesis)
   - [Postfix Expression Evaluation](src/_DataStructures_/Stack/postfix-expression-evaluation)
   - [Remove Consecutive Repeated Digits](src/_DataStructures_/Stack/remove-consecutive-repeated-digits)
   - [Implement 2 Stacks using Single Array](src/_DataStructures_/Stack/2-stacks-using1-array)
-  
 
 - [Queue](src/_DataStructures_/Queue)
+
   - [Weave](src/_DataStructures_/Queue/weave)
 
 - [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
-- [Suffix Tree](src/_DataStructures_/SuffixTree)
+
+- [Trees](src/_DataStructures_/Trees)
+  - [Binary Search Tree](src/_DataStructures_/Trees/BST)
+  - [Suffix Tree](src/_DataStructures_/SuffixTree)
 
 ### Logical Problems
 
@@ -67,7 +70,6 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 
 - [LRU Cache](src/_Algorithms_/lru-cache)
 
-
 ### Path Finder
 
 - [A\*](src/PathFinder/AStart)

src/_DataStructures_/Trees/BST/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/BST/index.js

@@ -0,0 +1,110 @@
+const Node = require('./Node');
+
+class BinarySearchTree {
+  constructor(value) {
+    this.root = new Node(value);
+  }
+
+  insert(root, value) {
+    if (root === null) {
+      const newNode = new Node(value);
+      // eslint-disable-next-line no-param-reassign
+      root = newNode;
+      return root;
+    }
+
+    if (value < root.value) {
+      // eslint-disable-next-line no-param-reassign
+      root.leftChild = this.insert(root.leftChild, value);
+      return root;
+    }
+    if (value > root.value) {
+      // eslint-disable-next-line no-param-reassign
+      root.rightChild = this.insert(root.rightChild, value);
+      return root;
+    }
+    return root;
+  }
+
+  preorder(root) {
+    /** returning an array so as to make testing easy */
+    let arr = [];
+    if (root === null) return [];
+    arr.push(root.value);
+
+    const left = this.preorder(root.leftChild);
+    arr = [...arr, ...left];
+
+    const right = this.preorder(root.rightChild);
+    arr = [...arr, ...right];
+    return arr;
+  }
+
+  inorder(root) {
+    /** left - root - right */
+    if (root === null) return [];
+    let arr = [];
+    const left = this.inorder(root.leftChild);
+    arr = [...left, ...arr];
+
+    // print root
+    arr = [...arr, root.value];
+
+    const right = this.inorder(root.rightChild);
+    arr = [...arr, ...right];
+    return arr;
+  }
+
+  postorder(root) {
+    /** left - right - root */
+
+    if (root === null) return [];
+    let arr = [];
+
+    const left = this.postorder(root.leftChild);
+    arr = [...left, ...arr];
+
+    const right = this.postorder(root.rightChild);
+    arr = [...arr, ...right];
+
+    return [...arr, root.value];
+  }
+
+  search(root, value) {
+    if (root === null) return false;
+    if (value === root.value) return true;
+
+    if (value < root.value) {
+      return this.search(root.leftChild, value);
+    }
+    if (value > root.value) {
+      return this.search(root.rightChild, value);
+    }
+    return false;
+  }
+}
+
+// const bst = new BinarySearchTree(6);
+// console.log(bst.root);
+// bst.insert(bst.root, 4);
+// bst.insert(bst.root, 9);
+// bst.insert(bst.root, 2);
+// bst.insert(bst.root, 5);
+// bst.insert(bst.root, 8);
+// bst.insert(bst.root, 12);
+
+// console.log(bst.root);
+
+// const preorder = bst.preorder(bst.root);
+// console.log('Preorder Traversal - ', preorder);
+
+// const inorder = bst.inorder(bst.root);
+// console.log('Inorder Traversal - ', inorder);
+
+// const postorder = bst.postorder(bst.root);
+// console.log('Postorder Traversal - ', postorder);
+
+// const search = 18;
+// console.log(`Search for ${search}`, bst.search(bst.root, search));
+
+module.exports = BinarySearchTree;