3 New Problems on BST

README.md

@@ -37,7 +37,12 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 - [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
 
 - [Trees](src/_DataStructures_/Trees)
-  - [Binary Search Tree](src/_DataStructures_/Trees/BST)
+  - [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)
+    - [Find Ancestors of a Node](src/_DataStructures_/Trees/BinarySearchTree/find-ancestors)
+    - [Find Height of BST](src/_DataStructures_/Trees/BinarySearchTree/height-of-bst)
+    - [Find k Nodes from Root of BST](src/_DataStructures_/Trees/BinarySearchTree/find-k-nodes-from-root)
   - [Suffix Tree](src/_DataStructures_/SuffixTree)
 
 ### Logical Problems

src/_DataStructures_/Trees/BinarySearchTree/find-ancestors/index.js

@@ -0,0 +1,49 @@
+// eslint-disable-next-line no-unused-vars
+const BST = require('../index');
+
+/** You should go through this conversation here:
+ * https://github.com/knaxus/problem-solving-javascript/pull/63
+ */
+
+function findAncestors(root, value) {
+  /**
+   * search the given node and meanwhile
+   * keep pushing the visited nodes
+   */
+  if (root === null) return false;
+
+  if (value < root.value) {
+    const left = findAncestors(root.leftChild, value);
+    if (left) {
+      return [...left, root.value];
+    }
+    return false;
+  }
+
+  if (value > root.value) {
+    const right = findAncestors(root.rightChild, value);
+    if (right) {
+      return [...right, root.value];
+    }
+    return false;
+  }
+
+  if (value === root.value) return [];
+  return false;
+}
+
+// create a BST
+// const myBST = new BST(6);
+// myBST.add(4);
+// myBST.add(9);
+// myBST.add(2);
+// myBST.add(5);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(12);
+// myBST.add(10);
+
+// console.log(findAncestors(myBST.root, 10));
+// console.log(findAncestors(myBST.root, 101));
+
+module.exports = findAncestors;

src/_DataStructures_/Trees/BinarySearchTree/find-k-nodes-from-root/index.js

@@ -0,0 +1,33 @@
+// eslint-disable-next-line no-unused-vars
+const BST = require('../index');
+
+function findKNodes(root, k) {
+  let arr = [];
+
+  if (root === null) return [];
+  if (k === 0) return [...arr, root.value];
+
+  const left = findKNodes(root.leftChild, k - 1);
+  arr = [...arr, ...left];
+
+  const right = findKNodes(root.rightChild, k - 1);
+  arr = [...arr, ...right];
+  return arr;
+}
+
+// create a BST
+// const myBST = new BST(6);
+
+// myBST.add(2);
+// myBST.add(19);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(5);
+// myBST.add(12);
+// myBST.add(33);
+// myBST.add(52);
+// myBST.add(1);
+
+// console.log(findKNodes(myBST.root, 2));
+
+module.exports = findKNodes;

src/_DataStructures_/Trees/BinarySearchTree/find-kth-max/index.js

@@ -0,0 +1,39 @@
+// eslint-disable-next-line no-unused-vars
+const BST = require('../index');
+
+// Inorder traversal returns a sorted array
+function inOrderTraversal(root) {
+  if (root === null) return [];
+  let arr = [];
+  // traverse left
+  const left = inOrderTraversal(root.leftChild);
+  arr = [...left, root.value];
+  const right = inOrderTraversal(root.rightChild);
+  return [...arr, ...right];
+}
+
+function findKthMax(rootNode, k) {
+  const arr = inOrderTraversal(rootNode);
+  if (k <= 0 || k > arr.lenth) {
+    throw new Error('Invalid value for K');
+  }
+  return arr[arr.length - k];
+}
+
+// // create a BST
+// const myBST = new BST(6);
+
+// myBST.add(2);
+// myBST.add(19);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(5);
+// myBST.add(12);
+// myBST.add(33);
+// myBST.add(52);
+// myBST.add(1);
+
+// // find 3rd max
+// console.log(findKthMax(myBST.root, 3));
+
+module.exports = findKthMax;

src/_DataStructures_/Trees/BinarySearchTree/find-kth-min/index.js

@@ -0,0 +1,39 @@
+// eslint-disable-next-line no-unused-vars
+const BST = require('../index');
+
+// Inorder traversal returns a sorted array
+function inOrderTraversal(root) {
+  if (root === null) return [];
+  let arr = [];
+  // traverse left
+  const left = inOrderTraversal(root.leftChild);
+  arr = [...left, root.value];
+  const right = inOrderTraversal(root.rightChild);
+  return [...arr, ...right];
+}
+
+function findKthMin(rootNode, k) {
+  const arr = inOrderTraversal(rootNode);
+  if (k <= 0 || k > arr.lenth) {
+    throw new Error('Invalid value for K');
+  }
+  return arr[k - 1];
+}
+
+// // create a BST
+// const myBST = new BST(6);
+
+// myBST.add(2);
+// myBST.add(19);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(5);
+// myBST.add(12);
+// myBST.add(33);
+// myBST.add(52);
+// myBST.add(1);
+// myBST.add(0);
+
+// console.log(findKthMin(myBST.root, 3));
+
+module.exports = findKthMin;

src/_DataStructures_/Trees/BinarySearchTree/height-of-bst/index.js

@@ -0,0 +1,33 @@
+// eslint-disable-next-line no-unused-vars
+const BST = require('../index');
+
+function findHeightOfBST(root) {
+  let leftHeight = 0;
+  let rightHeight = 0;
+
+  if (root === null) return 0;
+  leftHeight = findHeightOfBST(root.leftChild);
+  rightHeight = findHeightOfBST(root.rightChild);
+
+  if (leftHeight > rightHeight) {
+    return leftHeight + 1;
+  }
+  return rightHeight + 1;
+}
+
+// create a BST
+// const myBST = new BST(6);
+// myBST.add(4);
+// myBST.add(9);
+// myBST.add(2);
+// myBST.add(5);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(12);
+// myBST.add(10);
+
+// // console.log(myBST.root);
+// console.log(myBST.traversePreorder());
+// console.log(findHeightOfBST(myBST.root));
+
+module.exports = findHeightOfBST;