Added level order traversal

Author: linux-nerd

src/binary-search-tree/binary-search-tree.js

@@ -1,3 +1,4 @@
+import { Queue } from '../queue/queue';
 /**
  * This creates a node
  * @name BSTNode
@@ -38,6 +39,7 @@ export class BSTNode {
 const inOrderTraversal = Symbol('inorder');
 const preOrderTraversal = Symbol('preorder');
 const postOrderTraversal = Symbol('postorder');
+const levelOrderTraversal = Symbol('levelorder');
 
 /**
  * Private properties name
@@ -179,7 +181,7 @@ export class BST {
 
   /**
    * Print the values of the BST in specific order
-   * @param {string} type - value of type can be inOrder, preOrder, postOrder
+   * @param {string} type - value of type can be inOrder, preOrder, postOrder, levelOrder
    */
   traverse(type) {
     let retVal;
@@ -193,6 +195,9 @@ export class BST {
       case 'postOrder':
         retVal = this[postOrderTraversal]();
         break;
+      case 'levelOrder':
+        retVal = this[levelOrderTraversal]();
+        break;
       default:
         retVal = new Error('Type should be one of inOrder, preOrder or postOrder');
         break;
@@ -252,4 +257,31 @@ export class BST {
     recurseTraversal(subtree);
     return traversalList;
   }
+
+  /**
+   * Levelorder traversal - BFS
+   */
+  [levelOrderTraversal]() {
+    const bfsTraversalList = [];
+    const traversalQueue = new Queue;
+
+    if (this.root !== null) {
+      traversalQueue.enqueue(this.root);
+    }
+
+    while (!traversalQueue.isEmpty()) {
+      let presentNode = traversalQueue.top();
+      if (presentNode.left) {
+        traversalQueue.enqueue(presentNode.left);
+      }
+      if (presentNode.right) {
+        traversalQueue.enqueue(presentNode.right);
+      }
+      bfsTraversalList.push(presentNode.key);
+
+      traversalQueue.dequeue();
+    }
+
+    return bfsTraversalList;
+  }
 }

src/binary-search-tree/binary-search-tree.spec.js

@@ -155,5 +155,9 @@ describe('Binary Search Tree', () => {
     it('should return postorder list', () => {
       expect(bst.traverse('postOrder')).toEqual([5, 4, 10, 8, 6, 17, 31, 49, 43, 19, 11]);
     });
+
+    it('should return bfs list', () => {
+      expect(bst.traverse('levelOrder')).toEqual([11, 6, 19, 4, 8, 17, 43, 5, 10, 31, 49]);
+    });
   });
 });

typings/data-structures.d.ts

@@ -1,5 +1,5 @@
 declare namespace DataStructures {
-  interface BST {
+  class BST {
     insert(val: string | number, details?: object): void;
     lookup(val: string | number): { hasValue: boolean, currentNode: BST, parentNode: BST };
     traverse(type: string): Array<number | string> | Error;