BST Insert Operation in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given value.

DSA Javascript

function createNode(value) {
  return {
    value: value,
    left: null,
    right: null
  };
}

const newNode = [1](10);

Drag options to blanks, or click blank then click option'

AinsertNode

BNode

CcreateNode

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name that does not exist like insertNode.

Trying to use 'new' keyword with a plain object function.

The function to create a new node is named createNode, so calling createNode(10) creates the new node.

2fill in blank

medium

Complete the code to insert a value into the BST recursively.

DSA Javascript

function insertNode(root, value) {
  if (root === null) {
    return createNode(value);
  }
  if (value [1] root.value) {
    root.left = insertNode(root.left, value);
  } else {
    root.right = insertNode(root.right, value);
  }
  return root;
}

Drag options to blanks, or click blank then click option'

A===

B<

C>

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' causes wrong subtree traversal.

Using '===' or '!==' causes logic errors.

In BST, if the value to insert is less than the current node's value, we go to the left subtree.

3fill in blank

hard

Fix the error in the insert function to correctly handle duplicate values by ignoring them.

DSA Javascript

function insertNode(root, value) {
  if (root === null) {
    return createNode(value);
  }
  if (value < root.value) {
    root.left = insertNode(root.left, value);
  } else if (value > root.value) {
    root.right = insertNode(root.right, value);
  } else {
    [1];
  }
  return root;
}

Drag options to blanks, or click blank then click option'

Aroot.value = value

Breturn null

CinsertNode(root, value)

Dreturn root

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to insert duplicates again causing infinite recursion.

Replacing root.value overwrites existing node.

When the value equals root.value, we do nothing and return the current root to ignore duplicates.

4fill in blank

hard

Fill both blanks to insert multiple values into the BST using a loop.

DSA Javascript

function buildBST(values) {
  let root = null;
  for (let [1] = 0; [2] < values.length; [1]++) {
    root = insertNode(root, values[[1]]);
  }
  return root;
}

Drag options to blanks, or click blank then click option'

Ai

Bj

Cvalues.length

Droot

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong loop variable names inconsistently.

Incorrect loop condition causing infinite or no iteration.

The loop variable is 'i' and the condition is 'i < values.length' to iterate over all values.

5fill in blank

hard

Fill all three blanks to print the BST values in ascending order using in-order traversal.

DSA Javascript

function inOrderTraversal(root, result) {
  if (root !== null) {
    inOrderTraversal(root.[1], result);
    result.push(root.[2]);
    inOrderTraversal(root.[3], result);
  }
}

const result = [];
inOrderTraversal(bstRoot, result);
console.log(result);

Drag options to blanks, or click blank then click option'

Aleft

Bvalue

Cright

Droot

Attempts:

3 left

💡 Hint

Common Mistakes

Visiting right child before left causes descending order.

Pushing root instead of root.value causes wrong output.

In-order traversal visits left subtree, then node value, then right subtree to get sorted order.

Practice

1. What does the insert operation do in a Binary Search Tree (BST)?

easy

A. Searches for a node with a given value

B. Adds a new node in the correct position to maintain BST order

C. Deletes a node from the tree

D. Balances the tree automatically after insertion

Solution

1. Step 1: Understand BST property

   In a BST, left child nodes are smaller and right child nodes are larger than the parent node.

2. Step 2: Purpose of insert operation

   The insert operation places a new value in the tree so that this property remains true.

3. Final Answer:

   Adds a new node in the correct position to maintain BST order -> Option B

4. Quick Check:

   Insert means add node correctly [OK]

Hint: Insert means add node keeping BST order intact [OK]

Common Mistakes:

• Confusing insert with delete operation
• Thinking insert balances the tree automatically
• Assuming insert searches only without adding

2. Which of the following is the correct syntax to insert a value val into a BST node root in JavaScript?

easy

A. root = insert(root, val);

B. root.insert(val);

C. insert(root, val);

D. insert(val, root);

Solution

1. Step 1: Understand function usage in BST insert

   Insert usually returns the new root after insertion, so assignment is needed.

2. Step 2: Check parameter order and assignment

   The function takes the root and value, returns updated root, so root = insert(root, val); is correct.

3. Final Answer:

   root = insert(root, val); -> Option A

4. Quick Check:

   Assign updated root after insert [OK]

Hint: Insert returns new root, so assign it back [OK]

Common Mistakes:

• Calling insert without assignment
• Passing parameters in wrong order
• Using method call on root without method defined

3. What will be the inorder traversal output after inserting 5 into this BST?

    10
   /  
  3    15
   
    4

Insert 5 and then print inorder traversal.

medium

A. [3, 5, 4, 10, 15]

B. [3, 4, 10, 5, 15]

C. [3, 4, 5, 10, 15]

D. [5, 3, 4, 10, 15]

Solution

1. Step 1: Insert 5 into BST

   Start at root 10, 5 < 10 go left to 3, 5 > 3 go right to 4, 5 > 4 insert as right child of 4.

2. Step 2: Perform inorder traversal

   Inorder visits left, root, right: nodes visited in order: 3, 4, 5, 10, 15.

3. Final Answer:

   [3, 4, 5, 10, 15] -> Option C

4. Quick Check:

   Inorder sorted after insert [OK]

Hint: Inorder traversal of BST is sorted list [OK]

Common Mistakes:

• Inserting 5 as left child of 4
• Mixing preorder or postorder traversal output
• Ignoring BST property during insertion

4. Given this insert function snippet, what is the error?

function insert(root, val) {
  if (root == null) {
    return new Node(val);
  }
  if (val < root.val) {
    insert(root.left, val);
  } else {
    insert(root.right, val);
  }
  return root;
}

medium

A. Returning root before insertion

B. Incorrect base case condition

C. Using '==' instead of '===' for null check

D. Missing assignment of recursive insert result to root.left or root.right

Solution

1. Step 1: Check recursive calls

   Recursive calls to insert do not assign the returned node back to root.left or root.right, so tree structure won't update.

2. Step 2: Correct recursive assignment

   Should assign: root.left = insert(root.left, val); or root.right = insert(root.right, val); to update links.

3. Final Answer:

   Missing assignment of recursive insert result to root.left or root.right -> Option D

4. Quick Check:

   Assign recursive insert result to child [OK]

Hint: Always assign recursive insert result to child pointer [OK]

Common Mistakes:

• Ignoring assignment in recursion
• Confusing base case with recursive step
• Thinking '==' causes error here

5. You have a BST with nodes 20, 10, 30. You insert 25, then 5, then 35. What is the preorder traversal of the BST after all insertions?

hard

A. [20, 10, 5, 30, 25, 35]

B. [20, 30, 25, 35, 10, 5]

C. [10, 5, 20, 30, 25, 35]

D. [20, 10, 30, 5, 25, 35]

Solution

1. Step 1: Insert nodes step-by-step

   Start with root 20, left 10, right 30.
   Insert 25: 25 < 30 and > 20, goes left of 30.
   Insert 5: less than 10, goes left of 10.
   Insert 35: greater than 30, goes right of 30.

2. Step 2: Preorder traversal

   Preorder visits root, left subtree, right subtree.
   Visit 20, then left subtree (10, 5), then right subtree (30, 25, 35).
   So preorder: [20, 10, 5, 30, 25, 35]

3. Final Answer:

   [20, 10, 5, 30, 25, 35] -> Option A

4. Quick Check:

   Preorder = root-left-right [OK]

Hint: Preorder = root, left subtree, right subtree [OK]

Common Mistakes:

• Mixing preorder with inorder or postorder
• Inserting nodes in wrong position
• Forgetting to update tree after insert