Update ch4-q02.js

src/chapter4/ch4-q02.js

@@ -1,6 +1,45 @@
 'use strict';
 
-import { Tree } from './helpers';
+// import { Tree } from './helpers';
+
+
+// * The prior solution can be improved upon and run in
+// Time: O(N);
+// Space: O(N);
+/* A function that constructs Balanced Binary Search Tree
+    from a sorted array */
+
+export function main(arr) {
+  if (!arr || arr.length < 1) return null;
+
+  const tree = new BinaryTree();
+  //if its only one number its a node not a tree else create tree;
+  return  arr.length === 1 ? new Node(arr[0]) :
+      tree.createBst(arr, 0, arr.length - 1);
+  }
+
+class Node {
+  constructor(data) {
+    this.val = data;
+    this.left = this.right = null;
+  }
+}
+
+  class BinaryTree {
+
+  createBst(arr, start, end) {
+    if (start > end) return null;
+    const mid =  Math.floor((start + end) / 2),
+                node = new Node(arr[mid]);
+
+
+     node.left = this.createBst(arr, start, mid - 1);
+     node.right = this.createBst(arr, mid + 1, end);
+     return node;
+  }
+}
+
+
 
 /**
  * As the list is already sorted the best way to create a balanced tree is by
@@ -12,22 +51,22 @@ import { Tree } from './helpers';
  * Time: O(N lg N)
  * Additional space: O(N)
  */
-export function makeBalancedTree(values) {
-  let tree = new Tree();
-  if (values && values.length) {
-    add(tree, values, 0, values.length - 1);
-  }
-  return tree;
-}
+// export function makeBalancedTree(values) {
+//   let tree = new Tree();
+//   if (values && values.length) {
+//     add(tree, values, 0, values.length - 1);
+//   }
+//   return tree;
+// }
 
-function add(tree, values, start, end) {
-  if (start === end) {
-    tree.add(values[start]);
-  }
-  else if (start < end) {
-    let mid = start + Math.floor((end - start) / 2);
-    tree.add(values[mid]);
-    add(tree, values, start, mid - 1);
-    add(tree, values, mid + 1, end);
-  }
-}
+// function add(tree, values, start, end) {
+//   if (start === end) {
+//     tree.add(values[start]);
+//   }
+//   else if (start < end) {
+//     let mid = start + Math.floor((end - start) / 2);
+//     tree.add(values[mid]);
+//     add(tree, values, start, mid - 1);
+//     add(tree, values, mid + 1, end);
+//   }
+// }