Implement Binary Tree to Binary Search Tree Conversion - Solution

Author: k88manish

src/_Problems_/binary-tree-to-binary-search-tree/Node.js

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+module.exports = class Node {
+  constructor(value) {
+    this.value = value;
+    this.leftChild = null; // will be a node
+    this.rightChild = null; // will be a node
+  }
+};

src/_Problems_/binary-tree-to-binary-search-tree/binary-tree-to-binary-search-tree.test.js

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+const { binaryTreeToBST, storeInorder } = require('.');
+const Node = require('./Node');
+
+describe('Binary tree to binary search tree', () => {
+  let tree;
+
+  describe('Create Binary Tree', () => {
+    tree = new Node(10);
+    tree.leftChild = new Node(30);
+    tree.leftChild.leftChild = new Node(20);
+    tree.rightChild = new Node(15);
+    tree.rightChild.rightChild = new Node(5);
+  });
+
+  it('Should converted binary tree to binary search tree', () => {
+    binaryTreeToBST(tree);
+    expect(storeInorder(tree)).toEqual([5, 10, 15, 20, 30]);
+  });
+});

src/_Problems_/binary-tree-to-binary-search-tree/index.js

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+/**
+ * Given a Binary Tree, convert it to a Binary Search Tree.
+ * The conversion must be done in such a way that keeps the original structure of Binary Tree.
+ * Example 1
+Input:
+          10
+         /  \
+        2    7
+       / \
+      8   4
+Output:
+          8
+         /  \
+        4    10
+       / \
+      2   7
+ */
+
+// Helper function to store inorder traversal of a binary tree
+function storeInorder(root) {
+  /** left - root - right */
+  if (root === null) return [];
+
+  // First store the left subtree
+  let arr = [];
+  const left = storeInorder(root.leftChild);
+  arr = [...left, ...arr];
+
+  // Append root's data
+  arr = [...arr, root.value];
+
+  // Store right subtree
+  const right = storeInorder(root.rightChild);
+  arr = [...arr, ...right];
+  return arr;
+}
+
+// Helper function to copy elements from sorted array to make BST while keeping same structure
+function arrayToBST(arr, root) {
+  const node = root;
+  // Base case
+  if (!node) return;
+
+  // First update the left subtree
+  arrayToBST(arr, node.leftChild);
+
+  // update the root's data and remove it from sorted array
+  node.value = arr.shift();
+
+  // Finally update the right subtree
+  arrayToBST(arr, node.rightChild);
+}
+
+function binaryTreeToBST(root) {
+  // Tree is empty
+  if (!root) return;
+  const arr = storeInorder(root);
+  arr.sort((a, b) => a - b);
+  arrayToBST(arr, root);
+}
+
+module.exports = {
+  binaryTreeToBST,
+  storeInorder,
+};